gegl-imgcmp: Fix name of max-diff property
GLib 2.64 enforces the rules that were previously only documented for property and parameter names, resulting in this property not being looked up successfully, leaving uninitialized junk in the max_diff variable.
Signed-off-by: Simon McVittie smcv@debian.org
Resolves: #230 (closed)
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=954196