patch 8.2.4956: reading past end of line with "gf" in Visual block mode

Problem:    Reading past end of line with "gf" in Visual block mode.
Solution:   Do not include the NUL in the length.

src/normal.c

@@ -3671,9 +3671,16 @@ get_visual_text(
 	}
 	if (**pp == NUL)
 	    *lenp = 0;
-	if (has_mbyte && *lenp > 0)
+	if (*lenp > 0)
-	    // Correct the length to include all bytes of the last character.
+	{
-	    *lenp += (*mb_ptr2len)(*pp + (*lenp - 1)) - 1;
+	    if (has_mbyte)
+		// Correct the length to include all bytes of the last
+		// character.
+		*lenp += (*mb_ptr2len)(*pp + (*lenp - 1)) - 1;
+	    else if ((*pp)[*lenp - 1] == NUL)
+		// Do not include a trailing NUL.
+		*lenp -= 1;
+	}
     }
     reset_VIsual_and_resel();
     return OK;

src/testdir/test_gf.vim

@@ -138,6 +138,21 @@ func Test_gf_visual()
   call assert_equal('Xtest_gf_visual', bufname('%'))
   call assert_equal(3, getcurpos()[1])
 
+  " do not include the NUL at the end 
+  call writefile(['x'], 'X')
+  let save_enc = &enc
+  for enc in ['latin1', 'utf-8']
+    exe "set enc=" .. enc
+    new
+    call setline(1, 'X')
+    set nomodified
+    exe "normal \<C-V>$gf"
+    call assert_equal('X', bufname())
+    bwipe!
+  endfor
+  let &enc = save_enc
+  call delete('X')
+
   " line number in visual area is used for file name
   if has('unix')
     bwipe!

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4956,
 /**/
     4955,
 /**/