patch 8.2.3611: crash when using CTRL-W f without finding a file name

Problem:    Crash when using CTRL-W f without finding a file name.
Solution:   Bail out when the file name length is zero.

src/findfile.c

@@ -1735,6 +1735,9 @@ find_file_in_path_option(
     proc->pr_WindowPtr = (APTR)-1L;
 # endif
 
+    if (len == 0)
+	return NULL;
+
     if (first == TRUE)
     {
 	// copy file name into NameBuff, expanding environment variables
@@ -2118,7 +2121,12 @@ find_file_name_in_path(
     int		c;
 # if defined(FEAT_FIND_ID) && defined(FEAT_EVAL)
     char_u	*tofree = NULL;
+# endif
 
+    if (len == 0)
+	return NULL;
+
+# if defined(FEAT_FIND_ID) && defined(FEAT_EVAL)
     if ((options & FNAME_INCL) && *curbuf->b_p_inex != NUL)
     {
 	tofree = eval_includeexpr(ptr, len);

src/normal.c

@@ -3881,8 +3881,10 @@ get_visual_text(
 	    *pp = ml_get_pos(&VIsual);
 	    *lenp = curwin->w_cursor.col - VIsual.col + 1;
 	}
-	if (has_mbyte)
+	if (**pp == NUL)
-	    // Correct the length to include the whole last character.
+	    *lenp = 0;
+	if (has_mbyte && *lenp > 0)
+	    // Correct the length to include all bytes of the last character.
 	    *lenp += (*mb_ptr2len)(*pp + (*lenp - 1)) - 1;
     }
     reset_VIsual_and_resel();

src/testdir/test_visual.vim

@@ -1265,6 +1265,14 @@ func Test_visual_block_with_virtualedit()
   call delete('XTest_block')
 endfunc
 
+func Test_visual_block_ctrl_w_f()
+  " Emtpy block selected in new buffer should not result in an error.
+  au! BufNew foo sil norm f
+  edit foo
+
+  au! BufNew
+endfunc
+
 func Test_visual_reselect_with_count()
   " this was causing an illegal memory access
   let lines =<< trim END

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3611,
 /**/
     3610,
 /**/