Reset source to result group source when using search in push down (#2151)

- fix PushDownRefactoringProcessor.getReferencingElementsFromProject()
  method to reset the source string each time we look at a
  SearchResultGroup as the source may change from group to group and
  is not guaranteed to be the original compilation unit

Author: jjohnstn

org.eclipse.jdt.core.manipulation/refactoring/org/eclipse/jdt/internal/corext/refactoring/structure/PushDownRefactoringProcessor.java

@@ -393,6 +393,7 @@ private static IJavaElement[] getReferencingElementsFromProject(IMember member,
 		String source= cu.getSource();
 		CompilationUnit cuRoot= null;
 		for (SearchResultGroup group : (SearchResultGroup[]) engine.getResults()) {
+			source= group.getCompilationUnit().getSource();
 			for (SearchMatch searchResult : group.getSearchResults()) {
 				if (source.charAt(searchResult.getOffset() - 1) == '.') {
 					if (cuRoot == null) {