Do not use segment_info['buffer'].name ever

This results in UnicodeDecodeErrors for non-unicode filenames

powerline/segments/vim/__init__.py

@@ -489,7 +489,7 @@ def branch(pl, segment_info, create_watcher, status_colors=False):
 
 	Divider highlight group used: ``branch:divider``.
 	'''
-	name = segment_info['buffer'].name
+	name = buffer_name(segment_info)
 	skip = not (name and (not vim_getbufoption(segment_info, 'buftype')))
 	if not skip:
 		repo = guess(path=name, create_watcher=create_watcher)
@@ -513,7 +513,7 @@ def file_vcs_status(pl, segment_info, create_watcher):
 
 	Highlight groups used: ``file_vcs_status``.
 	'''
-	name = segment_info['buffer'].name
+	name = buffer_name(segment_info)
 	skip = not (name and (not vim_getbufoption(segment_info, 'buftype')))
 	if not skip:
 		repo = guess(path=name, create_watcher=create_watcher)

powerline/vim.py

@@ -146,23 +146,30 @@ class VimPowerline(Powerline):
 		self.update_renderer()
 		__main__.powerline = self
 
-		if (
-			bool(int(vim.eval("has('gui_running') && argc() == 0")))
-			and not vim.current.buffer.name
-			and len(vim.windows) == 1
-		):
-			# Hack to show startup screen. Problems in GUI:
-			# - Defining local value of &statusline option while computing global
-			#   value purges startup screen.
-			# - Defining highlight group while computing statusline purges startup
-			#   screen.
-			# This hack removes the “while computing statusline” part: both things 
-			# are defined, but they are defined right now.
-			#
-			# The above condition disables this hack if no GUI is running, Vim did 
-			# not open any files and there is only one window. Without GUI 
-			# everything works, in other cases startup screen is not shown.
-			self.new_window()
+		try:
+			if (
+				bool(int(vim.eval("has('gui_running') && argc() == 0")))
+				and not vim.current.buffer.name
+				and len(vim.windows) == 1
+			):
+				# Hack to show startup screen. Problems in GUI:
+				# - Defining local value of &statusline option while computing
+				#   global value purges startup screen.
+				# - Defining highlight group while computing statusline purges
+				#   startup screen.
+				# This hack removes the “while computing statusline” part: both 
+				# things are defined, but they are defined right now.
+				#
+				# The above condition disables this hack if no GUI is running, 
+				# Vim did not open any files and there is only one window. 
+				# Without GUI everything works, in other cases startup screen is 
+				# not shown.
+				self.new_window()
+		except UnicodeDecodeError:
+			# vim.current.buffer.name may raise UnicodeDecodeError when using 
+			# Python-3*. Fortunately, this means that current buffer is not 
+			# empty buffer, so the above condition should be False.
+			pass
 
 		# Cannot have this in one line due to weird newline handling (in :execute 
 		# context newline is considered part of the command in just the same cases