Fix database schema manager

1. Prepare the utf8mb4 conversion check table before the changeset is
created to avoid SQL error about not existing table when running schema
updates on a pre-3.5.0 database after having updated the files only to
3.5.0.
2. Run the conversion only if no unfixed database problems remained
after changeset fix().

administrator/components/com_installer/models/database.php

@@ -42,6 +42,10 @@ protected function populateState($ordering = null, $direction = null)
 		$this->setState('extension_message', $app->getUserState('com_installer.extension_message'));
 		$app->setUserState('com_installer.message', '');
 		$app->setUserState('com_installer.extension_message', '');
+
+		// Prepare the utf8mb4 conversion check table
+		$this->prepareUtf8mb4StatusTable();
+
 		parent::populateState('name', 'asc');
 	}
 
@@ -67,9 +71,16 @@ public function fix()
 		$installer->deleteUnexistingFiles();
 		$this->fixDefaultTextFilters();
 
-		// Finally make sure the database is converted to utf8mb4 or, if not suported
-		// by the server, compatible to it
-		$this->convertTablesToUtf8mb4();
+		/*
+		 * Finally, if the schema updates succeeded, make sure the database is
+		 * converted to utf8mb4 or, if not suported by the server, compatible to it.
+		 */
+		$statusArray = $changeSet->getStatus();
+
+		if (count($statusArray['error']) == 0)
+		{
+			$this->convertTablesToUtf8mb4();
+		}
 	}
 
 	/**