Preserve substitution flag value within the current line.

Fixed the following testcase
# cat strings |./busybox sed -n -f test3.sed
1
1
2
c
c
# cat strings
a
b
c

editors/sed.c

@@ -902,7 +902,7 @@ static void process_file(FILE * file)
 				}
 #endif
 					/* we print the pattern_space once, unless we were told to be quiet */
-					substituted = do_subst_command(sed_cmd, &pattern_space);
+					substituted |= do_subst_command(sed_cmd, &pattern_space);
 
 #ifdef CONFIG_FEATURE_SED_EMBEDED_NEWLINE
 					/* undo HACK: escape newlines twice so regex can match them */