Incorrect context path calculation for AJS.params

For Confluence installations where is no context path (so not http://example.com:8080/confluence/ but just http://example.com:8080/) the context path in AJS.params.contextPath is invalid and so if we try to call Macro Browser (in macro-browser.js):

url: AJS.params.contextPath + "/plugins/macrobrowser/browse-macros.action"

the resulting path is:

http://example.com:8080/pages/undefined/plugins/macrobrowser/browse-macros.action

instead of correct one http://example.com:8080/plugins/macrobrowser/browse-macros.action