Fix tab-completion crash when no results were returned.

IPython/core/completer.py

@@ -695,6 +695,7 b' class IPCompleter(Completer):'
             #print "try",c # dbg
             try:
                 res = c(event)
+                if res:
                 # first, try case sensitive match
                 withcase = [r for r in res if r.startswith(text)]
                 if withcase: