Avoid loplugin:staticmethods in non-debug build

Change-Id: I41cf1baa9899a4c8af3382b0c7c047348bf3498e

svx/source/form/fmshell.cxx

@@ -1426,6 +1426,8 @@ SdrUnoObj* FmFormShell::GetFormControl( const Reference< XControlModel >& _rxMod
             OSL_ENSURE( !pUnoObject, "FmFormShell::GetFormControl: the given control model belongs to a wrong page (displayed elsewhere)!" );
         }
     }
+#else
+    (void) this; // avoid loplugin:staticmethods
 #endif
 
     return NULL;