- Fix correctly MDEV-7498. The problem was not in AllocateValue but in

  the constructor of TYPVAL<PSZ> The new strg was widely uninitialised
  just by setting a terminated null char. Now the whole string is zero'ed.
  In Tabjson JSONCOL::ParseJpath, the original code was restored. 
modified:
  storage/connect/tabjson.cpp
  storage/connect/value.cpp

storage/connect/tabjson.cpp

@@ -508,13 +508,6 @@ bool JSONCOL::ParseJpath(PGLOBAL g)
   if (Parsed)
     return false;                       // Already done
 
-  if (InitValue(g))
-    return true;
-  else
-    MulVal = Value;
-
-  Value = NULL;
-
   if (InitValue(g))
     return true;
   else if (!Jpath)
@@ -548,6 +541,7 @@ bool JSONCOL::ParseJpath(PGLOBAL g)
 
     } // endfor i, p
 
+  MulVal = AllocateValue(g, Value);
   Parsed = true;
   return false;
   } // end of ParseJpath

storage/connect/value.cpp

@@ -1224,7 +1224,7 @@ TYPVAL<PSZ>::TYPVAL(PGLOBAL g, PSZ s, int n, int c)
   if (!s) {
     if (g) {
       if ((Strp = (char *)PlgDBSubAlloc(g, NULL, Len + 1)))
-        Strp[Len] = '\0';
+        memset(Strp, 0, Len + 1);
       else
         Len = 0;