Fix SpotBugs NP_ALWAYS_NULL warnings in Form and UIFragment

Fixes "Null pointer dereference" warnings reported by SpotBugs.
- In `Form.java`, fix potential NPE in `getFormLayeredPane` by handling the null case for class `c` correctly and safely handling `formLayeredPane` using a local variable.
- In `UIFragment.java`, initialize `el` before dereferencing it in `buildXMLFromJSONNotation` when the first element is not a String.
- Update `.github/scripts/generate-quality-report.py` to fail on `NP_ALWAYS_NULL` violations.

Author: google-labs-jules[bot]

CodenameOne/src/com/codename1/ui/Form.java

@@ -1584,11 +1584,7 @@ public void paintBackgrounds(Graphics g) {
             cnt.setWidth(getWidth());
             cnt.setHeight(getHeight());
             cnt.setShouldLayout(false);
-            if (c != null) {
-                cnt.setName("FormLayer: " + c.getName());
-            } else {
-                cnt.setName("FormLayer: null");
-            }
+            cnt.setName("FormLayer: null");
             flp.add(cnt);
             return cnt;
         }