vim: use try catch in vim plugin to avoid conflicts

contrib/vim/hgcommand.vim

@@ -105,7 +105,7 b' function! s:HGChangeToCurrentFileDir(fil'
   let fileName=<SID>HGResolveLink(a:fileName)
   let newCwd=fnamemodify(fileName, ':h')
   if strlen(newCwd) > 0
-    execute 'cd' escape(newCwd, ' ')
+    try | execute 'cd' escape(newCwd, ' ') | catch | | endtry
   endif
   return oldCwd
 endfunction
@@ -396,7 +396,7 b' function! s:HGGetStatusVars(revisionVar,'
 
     return returnExpression
   finally
-    execute 'cd' escape(oldCwd, ' ')
+    try | execute 'cd' escape(oldCwd, ' ') | catch | | endtry
   endtry
 endfunction