fixup! fixup! bpo-40585: Normalize errors messages in codeop when comparing them

Author: pablogsal

Parser/pegen/pegen.c

@@ -310,12 +310,12 @@ get_error_line(char *buffer, int is_file)
         newline = strchr(buffer, '\n');
     }
 
-    while (newline && *newline == '\n') {
-        newline -= 1;
+    while (is_file && newline > buffer && newline[-1] == '\n') {
+        --newline;
     }
 
     if (newline) {
-        return PyUnicode_DecodeUTF8(buffer, newline - buffer + 1, "replace");
+        return PyUnicode_DecodeUTF8(buffer, newline - buffer, "replace");
     }
     else {
         return PyUnicode_DecodeUTF8(buffer, strlen(buffer), "replace");