branches/5.1: fix bug#46256

Allow tables to be dropped even if the collation is not found,
but issue a warning.

Could not find an easy way to add mysql-test since it requires
changes to charsets and restarting the server. Tests were
executed manually.

Approved by: Heikki (on IM)

handler/ha_innodb.cc

@@ -818,7 +818,22 @@ innobase_get_cset_width(
 		*mbminlen = cs->mbminlen;
 		*mbmaxlen = cs->mbmaxlen;
 	} else {
-		ut_a(cset == 0);
+		if (current_thd
+		    && (thd_sql_command(current_thd) == SQLCOM_DROP_TABLE)) {
+
+			/* Fix bug#46256: allow tables to be dropped if the
+			collation is not found, but issue a warning. */
+			if ((global_system_variables.log_warnings)
+			    && (cset != 0)){
+
+				sql_print_warning(
+					"Unknown collation #%d.", cset);
+			}
+		} else {
+
+			ut_a(cset == 0);
+		}
+
 		*mbminlen = *mbmaxlen = 0;
 	}
 }