wrapGAppsHook: address some shellcheck suggestions

These should not cause issues in practice but it is good idea to handle them.

* prefix and targetOffset are mandatory, as they are always set by the generic builder.
* wrapPrefixVariables and dontWrapGApps are now defaulting to empty value, as they are not mandatory.

pkgs/build-support/setup-hooks/wrap-gapps-hook.sh

@@ -1,12 +1,13 @@
+# shellcheck shell=bash
 gappsWrapperArgs=()
 
 find_gio_modules() {
-    if [ -d "$1"/lib/gio/modules ] && [ -n "$(ls -A $1/lib/gio/modules)" ] ; then
+    if [ -d "$1/lib/gio/modules" ] && [ -n "$(ls -A "$1/lib/gio/modules")" ] ; then
         gappsWrapperArgs+=(--prefix GIO_EXTRA_MODULES : "$1/lib/gio/modules")
     fi
 }
 
-addEnvHooks "$targetOffset" find_gio_modules
+addEnvHooks "${targetOffset:?}" find_gio_modules
 
 wrapGApp() {
     local program="$1"
@@ -32,19 +33,19 @@ wrapGAppsHook() {
     gappsWrapperArgs+=(--prefix XDG_DATA_DIRS : "$GSETTINGS_SCHEMAS_PATH")
   fi
 
-  if [ -d "$prefix/share" ]; then
+  if [ -d "${prefix:?}/share" ]; then
     gappsWrapperArgs+=(--prefix XDG_DATA_DIRS : "$prefix/share")
   fi
 
-  if [ -d "$prefix/lib/gio/modules" ] && [ -n "$(ls -A $prefix/lib/gio/modules)" ] ; then
+  if [ -d "$prefix/lib/gio/modules" ] && [ -n "$(ls -A "$prefix/lib/gio/modules")" ] ; then
     gappsWrapperArgs+=(--prefix GIO_EXTRA_MODULES : "$prefix/lib/gio/modules")
   fi
 
-  for v in $wrapPrefixVariables GST_PLUGIN_SYSTEM_PATH_1_0 GI_TYPELIB_PATH GRL_PLUGIN_PATH; do
+  for v in ${wrapPrefixVariables:-} GST_PLUGIN_SYSTEM_PATH_1_0 GI_TYPELIB_PATH GRL_PLUGIN_PATH; do
-    gappsWrapperArgs+=(--prefix $v : "${!v}")
+    gappsWrapperArgs+=(--prefix "$v" : "${!v}")
   done
 
-  if [[ -z "$dontWrapGApps" ]]; then
+  if [[ -z "${dontWrapGApps:-}" ]]; then
     targetDirsThatExist=()
     targetDirsRealPath=()