patch 8.2.2758: Vim9: wrong line number for autoload function with wrong name

Problem:    Vim9: wrong line number for autoload function with wrong name.
Solution:   Set and restore SOURCING_LNUM. (closes #8100)
diff --git a/src/userfunc.c b/src/userfunc.c
index 54335d4..772d45d 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -4058,7 +4058,11 @@
 	    }
 	    if (j == FAIL)
 	    {
+		linenr_T save_lnum = SOURCING_LNUM;
+
+		SOURCING_LNUM = sourcing_lnum_top;
 		semsg(_("E746: Function name does not match script file name: %s"), name);
+		SOURCING_LNUM = save_lnum;
 		goto erret;
 	    }
 	}