Dumper: Fix exception when accessing empty items

This also fixes accessing 'this' when located inside a
different thread.

Task-number: QTCREATORBUG-18466
Change-Id: Ib90cc23c65c033a234d3f7cf9b1ba76abff719e2
Reviewed-by: hjk <hjk@qt.io>

share/qtcreator/debugger/dumper.py

@@ -577,6 +577,8 @@ class DumperBase:
         #warn("TARGS: %s %s" % (typename, targs))
         res = []
         for item in targs[::-1]:
+            if len(item) == 0:
+                continue
             c = ord(item[0])
             if c in (45, 46) or (c >= 48 and c < 58): # '-', '.' or digit.
                 if item.find('.') > -1: