Improve SafeRe code readability

function isSafePattern was never used as boolean function, its only
useful behaviour being raising exception on bad regexp, so it's renamed
and reused accordingly

plugins/Sidebar/ConsolePlugin.py

@@ -14,8 +14,7 @@ class WsLogStreamer(logging.StreamHandler):
         self.ui_websocket = ui_websocket
 
         if filter:
-            if not SafeRe.isSafePattern(filter):
-                raise Exception("Not a safe prex pattern")
+            SafeRe.guard(filter):
             self.filter_re = re.compile(".*" + filter)
         else:
             self.filter_re = None
@@ -55,7 +54,7 @@ class UiWebsocketPlugin(object):
         pos_start = log_file.tell()
         lines = []
         if filter:
-            assert SafeRe.isSafePattern(filter)
+            SafeRe.guard(filter)
             filter_re = re.compile(".*" + filter)
 
         last_match = False