CppEditor: Fix accessing null pointer...

...when executing FakeVim plugin unit tests.

Introduced with e50aafafe3

Change-Id: I8db057921d5adbcbe262a4dc0fee40378477694a
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/cppeditor/cppeditordocument.cpp

@@ -169,6 +169,7 @@ void CppEditorDocument::applyFontSettings()
         }
     }
     TextDocument::applyFontSettings(); // rehighlights and updates additional formats
+    if (m_processor)
         m_processor->semanticRehighlight();
 }