Add the Mem.szMalloc element to the Mem object and use it to keep track of

the size of the Mem.zMalloc allocation.

FossilOrigin-Name: 9c09ac353df6041808cace41880f4729ee73f5e1

src/test_func.c

@@ -504,7 +504,7 @@ static void test_extract(
       sqlite3_result_value(context, &mem);
     }
 
-    sqlite3DbFree(db, mem.zMalloc);
+    if( mem.szMalloc ) sqlite3DbFree(db, mem.zMalloc);
   }
 }
 
@@ -591,7 +591,7 @@ static void test_decode(
 
     Tcl_ListObjAppendElement(0, pRet, pVal);
 
-    if( mem.zMalloc ){
+    if( mem.szMalloc ){
       sqlite3DbFree(db, mem.zMalloc);
     }
   }