Fix GDrive handling of office files

1) Properly detect empty file extension, can be null.

2) When renaming part file to final file, use the correct file name
without extension, if it exists

3) When renaming a file, do not delete the original file if it had the
same id, which can happen with part files

apps/files_external/lib/google.php

@@ -264,7 +264,7 @@ public function opendir($path) {
 				foreach ($children->getItems() as $child) {
 					$name = $child->getTitle();
 					// Check if this is a Google Doc i.e. no extension in name
-					if ($child->getFileExtension() === ''
+					if (empty($child->getFileExtension())
 						&& $child->getMimeType() !== self::FOLDER
 					) {
 						$name .= '.'.$this->getGoogleDocExtension($child->getMimeType());
@@ -368,8 +368,14 @@ public function unlink($path) {
 	public function rename($path1, $path2) {
 		$file = $this->getDriveFile($path1);
 		if ($file) {
+			$newFile = $this->getDriveFile($path2);
 			if (dirname($path1) === dirname($path2)) {
-				$file->setTitle(basename(($path2)));
+				if ($newFile) {
+					// rename to the name of the target file, could be an office file without extension
+					$file->setTitle($newFile->getTitle());
+				} else {
+					$file->setTitle(basename(($path2)));
+				}
 			} else {
 				// Change file parent
 				$parentFolder2 = $this->getDriveFile(dirname($path2));
@@ -394,8 +400,11 @@ public function rename($path1, $path2) {
 			if ($result) {
 				$this->setDriveFile($path1, false);
 				$this->setDriveFile($path2, $result);
-				if ($oldfile) {
-					$this->service->files->delete($oldfile->getId());
+				if ($oldfile && $newFile) {
+					// only delete if they have a different id (same id can happen for part files)
+					if ($newFile->getId() !== $oldfile->getId()) {
+						$this->service->files->delete($oldfile->getId());
+					}
 				}
 			}
 			return (bool)$result;