permissions: Take PlistBuddy exit code into account when reading Info.plist

Otherwise we might conclude that we found a usage description when
PlistBuddy outputs "Error Reading File: /tmp/Info.plist" to stdout.

For CMake this is not an issue as we pipe stderr to a separate variable,
that contains "Cannot parse a NULL or zero-length data" in this case.

Fixes: QTBUG-109967
Pick-to: 6.5
Change-Id: I9d819b6de405b88bb7d1d75c22b6f5187f26e553
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

mkspecs/features/permissions.prf

@@ -6,14 +6,23 @@ for(plugin, QT_PLUGINS) {
         next()
 
     usage_descriptions = $$eval(QT_PLUGIN.$${plugin}.usage_descriptions)
+
+    found_usage_description = false
     for(usage_description_key, usage_descriptions) {
         usage_description = $$system("/usr/libexec/PlistBuddy" \
-        "-c 'print $$usage_description_key' $$QMAKE_INFO_PLIST 2>/dev/null")
-        !isEmpty(usage_description): \
+            "-c 'print $$usage_description_key' $$QMAKE_INFO_PLIST 2>/dev/null", \
+            singleLine, exit_code)
+
+        !equals(exit_code, 0): \
+            next()
+
+        !isEmpty(usage_description) {
+            found_usage_description = true
             break()
+        }
     }
 
-    isEmpty(usage_description): \
+    !$$found_usage_description: \
         next()
 
     request_flag = $$eval(QT_PLUGIN.$${plugin}.request_flag)