patch 8.2.3248: Vim9: error message for wrong input uses wrong line number

Problem:    Vim9: error message for wrong input uses wrong line number.
Solution:   Use the line number of the start of the command. (issue #8653)
diff --git a/src/vim9script.c b/src/vim9script.c
index 9b4a2c0..641b0dd 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -411,6 +411,7 @@
     int		mult = FALSE;
     garray_T	names;
     garray_T	as_names;
+    long	start_lnum = SOURCING_LNUM;
 
     tv.v_type = VAR_UNKNOWN;
     ga_init2(&names, sizeof(char_u *), 10);
@@ -511,6 +512,9 @@
     }
     cmd_end = arg;
 
+    // Give error messages for the start of the line.
+    SOURCING_LNUM = start_lnum;
+
     /*
      * find script file
      */