Make sure to not inject into a null-source

Author: MarcMil

soot-infoflow/src/soot/jimple/infoflow/AbstractInfoflow.java

@@ -540,7 +540,7 @@ private void patchDynamicInvokeInstructions() {
 				if (sm.hasActiveBody()) {
 					Body body = sm.getActiveBody();
 					patchDynamicInvokeInstructions(body);
-				} else if (!(sm.getSource() instanceof MethodSourceInjector)) {
+				} else if (!(sm.getSource() instanceof MethodSourceInjector) && sm.getSource() != null) {
 					sm.setSource(new MethodSourceInjector(sm.getSource()) {
 
 						@Override