patch 9.0.1573: error for function name has wrong line number

Problem:    Error for function name has wrong line number.
Solution:   Set the line number before giving the error.

src/testdir/test_vim9_func.vim

@@ -166,6 +166,14 @@ def Test_wrong_function_name()
   delfunc g:Define
 enddef
 
+def Test_listing_function_error()
+  var lines =<< trim END
+      var filler = 123
+      func DoesNotExist
+  END
+  v9.CheckDefExecFailure(lines, 'E123:', 2)
+enddef
+
 def Test_break_in_skipped_block()
   var lines =<< trim END
       vim9script

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1573,
 /**/
     1572,
 /**/

src/vim9execute.c

@@ -4448,6 +4448,7 @@ exec_instructions(ectx_T *ectx)
 		    CLEAR_FIELD(ea);
 		    ea.cmd = ea.arg = iptr->isn_arg.string;
 		    ga_init2(&lines_to_free, sizeof(char_u *), 50);
+		    SOURCING_LNUM = iptr->isn_lnum;
 		    define_function(&ea, NULL, &lines_to_free, 0);
 		    ga_clear_strings(&lines_to_free);
 		}