Fixed ext storage touch function to return true on success

Some ext storage impl didn't return true on success.

Fixes #5943 (Dropbox)
Fixes #6010 (WebDAV)

apps/files_external/lib/dropbox.php

@@ -269,7 +269,11 @@ class Dropbox extends \OC\Files\Storage\Common {
 	}
 
 	public function touch($path, $mtime = null) {
-		return false;
+		if ($this->file_exists($path)) {
+			return false;
+		} else {
+			$this->file_put_contents($path, '');
+		}
 	}
 
 }

apps/files_external/lib/swift.php

@@ -364,7 +364,7 @@ class Swift extends \OC\Files\Storage\Common {
 					'X-Object-Meta-Timestamp' => $mtime
 				)
 			);
-			$object->Update($settings);
+			return $object->Update($settings);
 		} else {
 			$object = $this->container->DataObject();
 			if (is_null($mtime)) {
@@ -377,7 +377,7 @@ class Swift extends \OC\Files\Storage\Common {
 					'X-Object-Meta-Timestamp' => $mtime
 				)
 			);
-			$object->Create($settings);
+			return $object->Create($settings);
 		}
 	}
 

apps/files_external/lib/webdav.php

@@ -234,6 +234,7 @@ class DAV extends \OC\Files\Storage\Common{
 		} else {
 			$this->file_put_contents($path, '');
 		}
+		return true;
 	}
 
 	public function getFile($path, $target) {