patch 9.1.1194: filetype: false positive help filetype detection

Problem:  filetype: false positive help filetype detection
Solution: Only detect a file as help if modeline appears either at start
          of line or is preceded by whitespace (zeertzjq).

closes: #16845

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: zeertzjq

runtime/filetype.vim

@@ -1,7 +1,7 @@
 " Vim support file to detect file types
 "
 " Maintainer:	The Vim Project <https://github.com/vim/vim>
-" Last Change:	2025 Mar 08
+" Last Change:	2025 Mar 10
 " Former Maintainer:	Bram Moolenaar <Bram@vim.org>
 
 " Listen very carefully, I will say this only once
@@ -53,7 +53,7 @@ endfunc
 
 " Vim help file, set ft explicitly, because 'modeline' might be off
 au BufNewFile,BufRead */doc/*.txt
-	\  if getline('$') =~ 'vim:.*\<\(ft\|filetype\)=help\>'
+	\  if getline('$') =~ '\(^\|\s\)vim:.*\<\(ft\|filetype\)=help\>'
 	\|   setf help
 	\| endif
 

src/testdir/test_filetype.vim

@@ -1634,11 +1634,22 @@ func Test_help_file()
   call assert_equal('help', &filetype)
   bwipe!
 
+  call writefile(['some text', 'Copyright: |manual-copyright| vim:ft=help:'],
+        \ 'doc/help1.txt', 'D')
+  split doc/help1.txt
+  call assert_equal('help', &filetype)
+  bwipe!
+
   call writefile(['some text'], 'doc/nothelp.txt', 'D')
   split doc/nothelp.txt
   call assert_notequal('help', &filetype)
   bwipe!
 
+  call writefile(['some text', '`vim:ft=help`'], 'doc/nothelp1.txt', 'D')
+  split doc/nothelp1.txt
+  call assert_notequal('help', &filetype)
+  bwipe!
+
   filetype off
   set modeline&
 endfunc

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1194,
 /**/
     1193,
 /**/