Convert heic image to png failing

[outlawtorn]

command:
gm convert lib/alpha.heic -resize 240x240 res.png
output:
gm convert: Number of images is not supported (lib/alpha.heic).

Is the heic image attached is an invalid heic image?
alpha.zip

mediainfo of file
General
Complete name : alpha.heic
Format : HEIF
Codec ID : mif1 (mif1/heic)
File size : 433 KiB

Image 1
ID : 1002
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main@L6.2@Main
Codec ID : hvc1
Codec ID/Info : High Efficiency Video Coding
Width : 1 440 pixels
Height : 960 pixels
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Stream size : 192 KiB (44%)
Default : No
Derived : 1009
Codec configuration box : hvcC

Image 2
ID : 1005
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main@L6.2@Main
Codec ID : hvc1
Codec ID/Info : High Efficiency Video Coding
Width : 1 440 pixels
Height : 960 pixels
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Stream size : 239 KiB (55%)
Default : No
Auxilary : 1008
Derived : 1009
Codec configuration box : hvcC

Image 3
ID : 1008
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main@L6@Main
Codec ID : hvc1
Codec ID/Info : High Efficiency Video Coding
Width : 1 440 pixels
Height : 960 pixels
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Stream size : 400 Bytes (0%)
Default : No
Auxilary for : 1005
Codec configuration box : hvcC

Image 4
ID : 1009
Format : Image Overlay
Width : 1 440 pixels
Height : 960 pixels
Stream size : 22.0 Bytes (0%)
Derived for : 1002,1005

=========== GM VERSION ===========:

GraphicsMagick 1.3.38 2022-03-26 Q16 http://www.GraphicsMagick.org/
Copyright (C) 2002-2022 GraphicsMagick Group.
Additional copyrights and licenses apply to this software.
See http://www.GraphicsMagick.org/www/Copyright.html for details.

Feature Support:
Native Thread Safe yes
Large Files (> 32 bit) yes
Large Memory (> 32 bit) yes
BZIP yes
DPS no
FlashPix no
FreeType yes
Ghostscript (Library) no
HEIF/HVEC ("HEIC") yes
JBIG yes
JPEG-2000 no
JPEG yes
JPEG XL no
Little CMS yes
Loadable Modules no
Solaris mtmalloc no
Google perftools tcmalloc no
OpenMP yes (201511 "4.5")
PNG yes
TIFF yes
TRIO no
Solaris umem no
WebP yes
WMF yes
X11 yes
XML yes
ZLIB yes

Host type: x86_64-pc-linux-gnu

Configured using the command:
./configure '--build' 'x86_64-linux-gnu' '--enable-shared' '--enable-static' '--enable-libtool-verbose' '--prefix=/usr' '--mandir=${prefix}/share/man' '--infodir=${prefix}/share/info' '--docdir=${prefix}/share/doc/graphicsmagick' '--with-gs-font-dir=/usr/share/fonts/type1/gsfonts' '--with-x' '--without-dps' '--without-modules' '--without-frozenpaths' '--with-webp=yes' '--with-zstd=yes' '--with-perl' '--with-perl-options=INSTALLDIRS=vendor' '--enable-quantum-library-names' '--with-quantum-depth=16' 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -ffile-prefix-map=/build/graphicsmagick-vK5lFw/graphicsmagick-1.4+really1.3.38=. -flto=auto -ffat-lto-objects -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security' 'LDFLAGS=-Wl,-Bsymbolic-functions -flto=auto -ffat-lto-objects -flto=auto -Wl,-z,relro -Wl,-z,now' 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' 'CXXFLAGS=-g -O2 -ffile-prefix-map=/build/graphicsmagick-vK5lFw/graphicsmagick-1.4+really1.3.38=. -flto=auto -ffat-lto-objects -flto=a

Final Build Parameters:
CC = gcc
CFLAGS = -fopenmp -g -O2 -ffile-prefix-map=/build/graphicsmagick-vK5lFw/graphicsmagick-1.4+really1.3.38=. -flto=auto -ffat-lto-objects -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security -Wall
CPPFLAGS = -Wdate-time -D_FORTIFY_SOURCE=2 -I/usr/include/freetype2 -I/usr/include/libxml2
CXX = g++
CXXFLAGS = -g -O2 -ffile-prefix-map=/build/graphicsmagick-vK5lFw/graphicsmagick-1.4+really1.3.38=. -flto=auto -ffat-lto-objects -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security
LDFLAGS = -Wl,-Bsymbolic-functions -flto=auto -ffat-lto-objects -flto=auto -Wl,-z,relro -Wl,-z,now
LIBS = -ljbig -lwebp -lwebpmux -lheif -lde265 -llcms2 -ltiff -lfreetype -ljpeg -lpng16 -lwmflite -lXext -lSM -lICE -lX11 -llzma -lbz2 -lxml2 -lz -lzstd -lm -lpthread

[bobfriesenhahn]

The HEIF reader (user contributed source code) did not support multiple image frames and in fact rejects the input, even though it could have read the first frame. I plan on adding support for that, and much more.