patch 8.2.4979: accessing freed memory when line is flushed

Problem:    Accessing freed memory when line is flushed.
Solution:   Make a copy of the pattern to search for.

src/testdir/test_tagjump.vim

@@ -1392,6 +1392,15 @@ func Test_macro_search()
   close!
 endfunc
 
+func Test_define_search()
+  " this was accessing freed memory
+  new
+  call setline(1, ['first line', '', '#define something 0'])
+  sil norm o0
+  sil! norm 
+  bwipe!
+endfunc
+
 " Test for [*, [/, ]* and ]/
 func Test_comment_search()
   new

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4979,
 /**/
     4978,
 /**/

src/window.c

@@ -579,9 +579,16 @@ do_window(
 		CHECK_CMDWIN;
 		if ((len = find_ident_under_cursor(&ptr, FIND_IDENT)) == 0)
 		    break;
+
+		// Make a copy, if the line was changed it will be freed.
+		ptr = vim_strnsave(ptr, len);
+		if (ptr == NULL)
+		    break;
+
 		find_pattern_in_path(ptr, 0, len, TRUE,
 			Prenum == 0 ? TRUE : FALSE, type,
 			Prenum1, ACTION_SPLIT, (linenr_T)1, (linenr_T)MAXLNUM);
+		vim_free(ptr);
 		curwin->w_set_curswant = TRUE;
 		break;
 #endif