roundtrip for absolute/relative

Author: Siedlerchr

jabgui/src/main/java/org/jabref/gui/libraryproperties/general/GeneralPropertiesViewModel.java

@@ -271,7 +271,8 @@ public void togglePath(StringProperty fileDirectory) {
             if (!currPath.isAbsolute()) {
                 newPath = parentPath.resolve(fileDirectory.get()).toAbsolutePath().toString();
             } else if (currPath.isAbsolute()) {
-                newPath = parentPath.relativize(currPath).toString();
+                Path rel = parentPath.relativize(currPath);
+                newPath = rel.toString().isEmpty() ? "." : rel.toString();
             } else {
                 // case: convert to relative path and currPath is relative
                 return;