Ensure that ALTER TABLE commands open statement transactions. Fix for [596d059a].

FossilOrigin-Name: 0f2129f59f7df929106e2af876c2976dea6528c1dc1850d64cddb256f20e121a

src/alter.c

@@ -166,15 +166,15 @@ void sqlite3AlterRenameTable(
   }
 #endif
 
-  /* Begin a transaction for database iDb. 
-  ** Then modify the schema cookie (since the ALTER TABLE modifies the
-  ** schema). Open a statement transaction if the table is a virtual
-  ** table.
-  */
+  /* Begin a transaction for database iDb. Then modify the schema cookie
+  ** (since the ALTER TABLE modifies the schema). Call sqlite3MayAbort(),
+  ** as the scalar functions (e.g. sqlite_rename_table()) invoked by the 
+  ** nested SQL may raise an exception.  */
   v = sqlite3GetVdbe(pParse);
   if( v==0 ){
     goto exit_rename_table;
   }
+  sqlite3MayAbort(pParse);
 
   /* figure out how many UTF-8 characters are in zName */
   zTabName = pTab->zName;
@@ -243,7 +243,6 @@ void sqlite3AlterRenameTable(
     int i = ++pParse->nMem;
     sqlite3VdbeLoadString(v, i, zName);
     sqlite3VdbeAddOp4(v, OP_VRename, i, 0, 0,(const char*)pVTab, P4_VTAB);
-    sqlite3MayAbort(pParse);
   }
 #endif
 
@@ -564,6 +563,7 @@ void sqlite3AlterRenameColumn(
   ** uses the sqlite_rename_column() SQL function to compute the new
   ** CREATE statement text for the sqlite_master table.
   */
+  sqlite3MayAbort(pParse);
   zNew = sqlite3NameFromToken(db, pNew);
   if( !zNew ) goto exit_rename_column;
   assert( pNew->n>0 );