if() used at HB_P_FUNCTION to avoid a function call when not needed

harbour/source/vm/hvm.c

@@ -584,7 +584,9 @@ void HB_EXPORT hb_vmExecute( const BYTE * pCode, PHB_SYMB pSymbols )
             break;
 
          case HB_P_FUNCTION:
-            hb_itemClear( &hb_stack.Return );
+            if( ( &hb_stack.Return )->type )
+               hb_itemClear( &hb_stack.Return );
+
             hb_vmDo( pCode[ w + 1 ] + ( pCode[ w + 2 ] * 256 ) );
             hb_itemCopy( hb_stackTopItem(), &hb_stack.Return );
             hb_stackPush();
@@ -4736,4 +4738,4 @@ void HB_EXPORT hb_vmProcessDllSymbols( PHB_SYMB pModuleSymbols, USHORT uiModuleS
              hb_dynsymNew( ( pModuleSymbols + ui ) );
       }
    }
-}
+}