PD: Check threadType before using to index

Coverity issue 545314

src/Mod/PartDesign/App/FeatureHole.cpp

@@ -1371,6 +1371,9 @@ void Hole::findClosestDesignation()
     // Intended for thread type changes
     // finds the closest diameter of the new thread type
     int threadType = ThreadType.getValue();
+    if (threadType == -1) {
+        throw Base::IndexError(QT_TRANSLATE_NOOP("Exception", "Thread type is invalid"));
+    }
     int closestSize = 0;
     double diameter = ThreadDiameter.getValue();
     if (diameter == 0)