Fix a minor bug (#524)

autoload/vimtex/format.vim

@@ -17,7 +17,7 @@ function! vimtex#format#init_script() " {{{1
         \ '%(\\\[|\$\$)\s*$',
         \], '|') . ')'
 
-  let s:border_end = '\\%(' . join([
+  let s:border_end = '\v\\%(' . join([
         \   '\\\*?',
         \   'clear%(double)?page',
         \   'linebreak',
@@ -103,6 +103,9 @@ function! s:format(top, bottom) " {{{1
 
     " Skip all lines with comments
     if l:line =~# '\v%(^|[^\\])\%'
+      if l:current < l:mark
+        let l:bottom += s:format_build_lines(l:current+1, l:mark)
+      endif
       let l:mark = l:current - 1
       continue
     endif

test/vader/format.vader

@@ -84,7 +84,8 @@ Expect tex (Verify):
       nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed
       diam voluptua. At vero eos et accusam et justo duo dolores et ea \\
       rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem
-    \item ipsum dolor sit amet. start a new paragraph % test
+    \item ipsum dolor sit amet.
+      start a new paragraph % test
       Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
       eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
       voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet