[core/input] More robust event reading

Regular i3bar events *can* contain the character [, so a better
mechanism for detecting the initial opening [ is required. For now, do a
minimal change that requires the line to *start* with [. This should
never be the case for i3bar events, which are always JSON objects.

fixes #318

bumblebee/input.py

@@ -34,7 +34,7 @@ def read_input(inp):
             continue
         for fileno, event in events:
             line = "["
-            while "[" in line:
+            while line.startswith("["):
                 line = sys.stdin.readline().strip(",").strip()
             inp.has_event = True
             try: