gotta-patch-em: Fix wrong config setting

[why]
The config.cfg settings can be wrong if the to-be-patched font does not
set its own. The previous settings are never cleared, so that the flags
leak into the next font(s).

This is only relevant when the run is not parallel (i.e. no -j given) and
all fonts are patched sequentially in the same shell.
On parallel runs (like the release process) this is not a problem
because each patcher runs in its own subshell.

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

bin/scripts/gotta-patch-em-all-font-patcher!.sh

@@ -211,6 +211,7 @@ function patch_font {
 
   # source the font config file if exists:
   # fetches for example config_patch_flags
+  unset config_patch_flags
   if [ -f "$config_dir/config.cfg" ]
   then
     # shellcheck source=/dev/null