patch 8.2.5050: using freed memory when searching for pattern in path

Problem:    Using freed memory when searching for pattern in path.
Solution:   Make a copy of the line.

src/testdir/test_tagjump.vim

@@ -1290,6 +1290,17 @@ func Test_inc_search()
   close!
 endfunc
 
+" this was using a line from ml_get() freed by the regexp
+func Test_isearch_copy_line()
+  new
+  norm o
+  norm 0
+  0norm o
+  sil! norm bc0
+  sil! isearch \%')
+  bwipe!
+endfunc
+
 " Test for :dsearch, :dlist, :djump and :dsplit commands
 " Test for [d, ]d, [D, ]D, [ CTRL-D, ] CTRL-D and CTRL-W d commands
 func Test_macro_search()