Apply Fx25 tree-row fix to Windows only, and fix spacing there too

"height: auto" (from another extension's fix for this) actually caused
the bottoms of tree rows to be cut off on Windows (and at least on one
Linux installation with Chinese characters).
Do not show SSL error message for other network errors
Merge pull request #411 from aurimasv/webdav-ssl

Do not show SSL error message for other network errors
Remove unnecessary 'return;'
Tweak the tree row height a bit on Windows
Fix error merging items with relations in unsynced library
Better fix for merging items in unsynced libraries

Addresses a79872436
Check network errors against SEC error set as well
Merge pull request #412 from aurimasv/webdav-sec

Check network errors against SEC error set as well
Merge branch '4.0' of https://github.com/zotero/zotero into dev