patch 8.2.4938: crash when matching buffer with invalid pattern

Problem:    Crash when matching buffer with invalid pattern.
Solution:   Check for NULL regprog.
diff --git a/src/buffer.c b/src/buffer.c
index 35711f5..dfdb0c4 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2932,7 +2932,7 @@
 
     // First try the short file name, then the long file name.
     match = fname_match(rmp, buf->b_sfname, ignore_case);
-    if (match == NULL)
+    if (match == NULL && rmp->regprog != NULL)
 	match = fname_match(rmp, buf->b_ffname, ignore_case);
 
     return match;
diff --git a/src/testdir/test_buffer.vim b/src/testdir/test_buffer.vim
index aea3995..55ef0fd 100644
--- a/src/testdir/test_buffer.vim
+++ b/src/testdir/test_buffer.vim
@@ -415,6 +415,10 @@
   vsplit 0000000
   silent! buf [0--]\&\zs*\zs*e
   bwipe!
+
+  vsplit 00000000000000000000000000
+  silent! buf [0--]\&\zs*\zs*e
+  bwipe!
 endfunc
 
 " Test for the 'maxmem' and 'maxmemtot' options
diff --git a/src/version.c b/src/version.c
index 8cc9ceb..0a3a5df 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4938,
+/**/
     4937,
 /**/
     4936,