Changed GetTrajectoryTags() to EAFP-style.

Instead of using an if-check, GetTrajectoryTags() now just tries
JSON deserialization and catches a ValueError. This is more robust as
it also catches situations where the deserialization fails due to the
trajectory description being invalid or whitespace, but not None.

Author: psigen

src/prpy/util.py

@@ -229,11 +229,9 @@ def GetTrajectoryTags(traj):
     """
     import json
 
-    description = traj.GetDescription()
-
-    if description:
-        return json.loads(description)
-    else:
+    try:
+        return json.loads(traj.GetDescription())
+    except ValueError:
         return dict()