patch 8.2.4305: tex filetype detection fails

Problem:    Tex filetype detection fails.
Solution:   Check value to be positive. (closes #9704)
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 6f4a425..b9909c6 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -1306,4 +1306,23 @@
   filetype off
 endfunc
 
+func Test_tex_file()
+  filetype on
+
+  " only tests one case, should do more
+  let lines =<< trim END
+      % This is a sentence.
+
+      This is a sentence.
+  END
+  call writefile(lines, "Xfile.tex")
+  split Xfile.tex
+  call assert_equal('plaintex', &filetype)
+  bwipe
+
+  call delete('Xfile.tex')
+  filetype off
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 3df4cfc..3d72eca 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4305,
+/**/
     4304,
 /**/
     4303,