patch 8.2.3144: Vim9: no error when using an invalid value for a line number

Problem:    Vim9: no error when using an invalid value for a line number.
Solution:   Give an error if the string value is not recognized.
            (closes #8536)
diff --git a/src/eval.c b/src/eval.c
index 4d94d67..6537ffe 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -5376,6 +5376,8 @@
 	}
 	return &pos;
     }
+    if (in_vim9script())
+	semsg(_(e_invalid_value_for_line_number_str), name);
     return NULL;
 }