plugin: do not <END> when breaking a line in the middle

Port of Thyrum/vim-stabs#5.

plugin/smarttabs.vim

@@ -279,7 +279,14 @@ if ! exists('g:ctab_disable_checkalign') || g:ctab_disable_checkalign==0
       endif
       return "\<CR>"
     else
-      return "\<CR>\<c-r>=".s:SID().'CheckAlign(line(''.''))'."\<CR>\<END>"
+      let l:cursoradj = ""
+      let l:restofline = getline('.')[col('.') - 1:]
+      if len(l:restofline) && l:restofline !~ '^\s*$'
+        " adjust cursor position (go to first nonblank) only if the line was
+        " broken in the middle, i.e. if we have text after cursor
+        let l:cursoradj = "\<ESC>:normal!^\<CR>:startinsert\<CR>"
+      endif
+      return "\<CR>\<c-r>=".s:SID().'CheckAlign(line(''.''))'."\<CR>\<END>" . l:cursoradj
     endif
   endfun