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);