The changes module crashed on empty commit/revision lists (Fixes #68).

Once again introduced with aeb9ad6, this could happen whenever a
repository had no commits or if the history was being filtered with
--since and/or --until and no commits were being detected within that
interval.

gitinspector/changes.py

@@ -185,12 +185,14 @@ class Changes:
 	emails_by_author = {}
 
 	def __init__(self, hard):
-
+		self.commits = []
 		git_log_hashes_r = subprocess.Popen(filter(None, ["git", "rev-list", "--reverse", "--no-merges",
 		                                    interval.get_since(), interval.get_until(), "HEAD"]), bufsize=1,
 		                                    stdout=subprocess.PIPE).stdout
 		lines = git_log_hashes_r.readlines()
 		git_log_hashes_r.close()
+
+		if len(lines) > 0:
 			self.commits = [None] * (len(lines) // CHANGES_PER_THREAD + 1)
 			first_hash = ""
 
@@ -209,12 +211,12 @@ class Changes:
 		for i in range(0, NUM_THREADS):
 			__thread_lock__.acquire()
 
+		if len(self.commits) > 0:
 			self.commits = [item for sublist in self.commits for item in sublist]
 
 			if interval.has_interval() and len(self.commits) > 0:
 				interval.set_ref(self.commits[-1].sha)
 
-		if len(self.commits) > 0:
 			self.first_commit_date = datetime.date(int(self.commits[0].date[0:4]), int(self.commits[0].date[5:7]),
 			                                       int(self.commits[0].date[8:10]))
 			self.last_commit_date = datetime.date(int(self.commits[-1].date[0:4]), int(self.commits[-1].date[5:7]),