Strip whitespaces from URL and dirname prior to extension installation

This avoid some cryptic errors brought by accidental spaces around urls

modules/ui_extensions.py

@@ -325,6 +325,11 @@ def normalize_git_url(url):
 def install_extension_from_url(dirname, url, branch_name=None):
     check_access()
 
+    if isinstance(dirname, str):
+        dirname = dirname.strip()
+    if isinstance(url, str):
+        url = url.strip()
+
     assert url, 'No URL specified'
 
     if dirname is None or dirname == "":