Fix crash in include completion with non-canonical include paths

Use QFileInfo::fileName() to get the filename, since that also works
when the original path wasn't canonical.

src/plugins/cpptools/cppmodelmanagerinterface.h

@@ -41,7 +41,7 @@ namespace ProjectExplorer {
 }
 
 namespace CppTools {
-    
+
 class AbstractEditorSupport;
 
 class CPPTOOLS_EXPORT CppModelManagerInterface : public QObject