Fix regexp when non-ruby thread received the signal

A space is added only when the source path is found.

Author: nobu

test/ruby/test_rubyoptions.rb

@@ -791,7 +791,7 @@ module SEGVTest
     # see assert_pattern_list
     ExpectedStderrList = [
       %r(
-        (?:-e:(?:1:)?)?\s\[BUG\]\sSegmentation\sfault.*\n
+        (?:-e:(?:1:)?\s)?\[BUG\]\sSegmentation\sfault.*\n
       )x,
       %r(
         #{ Regexp.quote(RUBY_DESCRIPTION) }\n\n