MDEV-36248 Connect crashes server because of duplicate 'free()' in GetUser

If connect engineis not able to allocate connect_work_space memory for
GetUser() it will call free() twice with the same value (g).

g was freed first in user_connect::user_init() which calls PlugExit() on
errors and then again in ~user_connect() which also calls PlugExit().

Fixed by setting g to 0 in user_init() after calling PlugExit()
This code was tested 'by hand' by setting connect.work_space=600G

Other things:
- Removed some very old not relevant comments in touched code
- Added comments to clarify how some memory was freed
- Fixed indentation in changed functions.

Author: montywi

storage/connect/connect.cc

@@ -92,11 +92,11 @@ void CntEndDB(PGLOBAL g)
 
     free(dbuserp);
 
-		if (trace(1))
-			htrc("CntEndDB: Freeing Dup\n");
+    if (trace(1))
+      htrc("CntEndDB: Freeing Dup\n");
 
-		g->Activityp->Aptr = NULL;
-	} // endif dbuserp
+    g->Activityp->Aptr = NULL;                  // Free PlgGetUser() data
+  } // endif dbuserp
 
 } // end of CntEndDB
 

storage/connect/user_connect.cc

@@ -101,9 +101,6 @@ bool user_connect::user_init()
   PACTIVITY ap= NULL;
   PDBUSER   dup= NULL;
 
-  // Areasize= 64M because of VEC tables. Should be parameterisable
-//g= PlugInit(NULL, 67108864);
-//g= PlugInit(NULL, 134217728);  // 128M was because of old embedded tests
   g= PlugInit(NULL, (size_t)worksize);
 
   // Check whether the initialization is complete
@@ -113,12 +110,13 @@ bool user_connect::user_init()
       printf("%s\n", g->Message);
 
     (void) PlugExit(g);
+    g= 0;
 
-		if (dup)
-	    free(dup);
+    if (dup)
+      free(dup);
 
     return true;
-    } // endif g->
+  } // endif g->
 
   dup->Catalog= new MYCAT(NULL);
 
@@ -128,17 +126,16 @@ bool user_connect::user_init()
   g->Activityp= ap;
   g->Activityp->Aptr= dup;
 
-	pthread_mutex_lock(&usrmut);
+  pthread_mutex_lock(&usrmut);
   next= to_users;
   to_users= this;
 
   if (next)
     next->previous= this;
 
-	count = 1;
-	pthread_mutex_unlock(&usrmut);
-
-	last_query_id= thdp->query_id;
+  count = 1;
+  pthread_mutex_unlock(&usrmut);
+  last_query_id= thdp->query_id;
   return false;
 } // end of user_init