Fix "Undefined variable: main_syntax".

StanAngeloff · StanAngeloff · commit 8ebb0e1b2ce8 · 2016-03-07T10:48:46.000+02:00
Closes StanAngeloff#50.
diff --git a/syntax/php.vim b/syntax/php.vim
@@ -847,7 +847,7 @@ let b:current_syntax = "php"
 let &iskeyword = s:iskeyword_save
 unlet s:iskeyword_save
 
-if main_syntax == 'php'
+if (exists("main_syntax") && main_syntax == 'php')
   unlet main_syntax
 endif
 
