Guard against empty search pattern in 'mc/mark-all-in-region', otherwise it will enter an infinite loop
Abort immediately when empty search pattern is passed to 'mc/mark-all-in-region'
Guard with 'if' rather than defun*/return-from
Merge pull request #109 from mathrick/fix-mark-all-in-region-hang

Guard against empty search pattern in 'mc/mark-all-in-region', otherwise...