Most Guix system setup with desktop evironment will install GDK_PIXBUF_MODULE_FILE
environment variable in the system profile, and it'll be leaked into the sandbox
environment of flatpak, so the applications in sandbox may fail to find correct
GdkPixbuf loaders.

This patch unset the GDK_PIXBUF_MODULE_FILE environment variable before running
the sandboxed applications, prevents it to load GdkPixbuf loaders from the path
of host system.

--- a/common/flatpak-run.c
+++ b/common/flatpak-run.c
@@ -1900,8 +1900,9 @@ static const ExportData default_exports[] = {
   {"XKB_CONFIG_ROOT", NULL},
   {"GIO_EXTRA_MODULES", NULL},
   {"GDK_BACKEND", NULL},
+  {"GDK_PIXBUF_MODULE_FILE", NULL},
   {"VK_DRIVER_FILES", NULL},
   {"VK_ICD_FILENAMES", NULL},
 };
 
 static const ExportData no_ld_so_cache_exports[] = {
ect> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=0e5539148244077215a984af9347a739c65e7ccb'>refs</a><a class='active' href='/guix/log/etc/guix-gc.timer'>log</a><a href='/guix/tree/etc/guix-gc.timer?id=0e5539148244077215a984af9347a739c65e7ccb'>tree</a><a href='/guix/commit/etc/guix-gc.timer?id=0e5539148244077215a984af9347a739c65e7ccb'>commit</a><a href='/guix/diff/etc/guix-gc.timer?id=0e5539148244077215a984af9347a739c65e7ccb'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/etc/guix-gc.timer'>
<input type='hidden' name='id' value='0e5539148244077215a984af9347a739c65e7ccb'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=0e5539148244077215a984af9347a739c65e7ccb'>root</a>/<a href='/guix/log/etc?id=0e5539148244077215a984af9347a739c65e7ccb'>etc</a>/<a href='/guix/log/etc/guix-gc.timer?id=0e5539148244077215a984af9347a739c65e7ccb'>guix-gc.timer</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/etc/guix-gc.timer?id=0e5539148244077215a984af9347a739c65e7ccb&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-09-20 14:18:21 +0000'>2021-09-20</span></td><td><a href='/guix/commit/etc/guix-gc.timer?id=5c4fd77097e2cecfd4780e099af7954f86779fe1'>etc: Add systemd files for running ‘guix gc’ periodically</a><span class='msg-avail'>...</span></td><td>Thiago Jung Bauermann</td></tr>