swaylock: Allow for transparent color values

There is only a slight issue. When using a transparent color the views
are arranged to make room for swaylock which we can now see. I tried removing
the arrange call but that just made it worse by putting in an opaque view on the
workspace and not making the lockoverlay color. Ill raise an issue if
this is not easily solved

swaylock/main.c

@@ -211,12 +211,12 @@ int main(int argc, char **argv) {
 	const char *usage =
 		"Usage: swaylock [options...]\n"
 		"\n"
-		"  -h, --help             Show help message and quit.\n"
-		"  -c, --color <rrggbb>   Turn the screen into the given color instead of white.\n"
-		"  -s, --scaling          Scaling mode: stretch, fill, fit, center, tile.\n"
-		"  -t, --tiling           Same as --scaling=tile.\n"
-		"  -v, --version          Show the version number and quit.\n"
-		"  -i, --image <path>     Display the given image.\n";
+		"  -h, --help                 Show help message and quit.\n"
+		"  -c, --color <rrggbb[aa]>   Turn the screen into the given color instead of white.\n"
+		"  -s, --scaling              Scaling mode: stretch, fill, fit, center, tile.\n"
+		"  -t, --tiling               Same as --scaling=tile.\n"
+		"  -v, --version              Show the version number and quit.\n"
+		"  -i, --image <path>         Display the given image.\n";
 
 	int c;
 	while (1) {
@@ -226,16 +226,22 @@ int main(int argc, char **argv) {
 			break;
 		}
 		switch (c) {
-		case 'c':
-			if (strlen(optarg) < 6) {
-				fprintf(stderr, "color must be specified in 3 byte format, e.g. ff0000\n");
+		case 'c': 
+		{
+			int colorlen = strlen(optarg);
+			if (colorlen < 6 || colorlen == 7 || colorlen > 8) {
+				fprintf(stderr, "color must be specified in 3 or 4 byte format, e.g. ff0000 or ff0000ff\n");
 				exit(EXIT_FAILURE);
 			}
 			color = strtol(optarg, NULL, 16);
-			color <<= 8;
-			color |= 0xFF;
+
+			if (colorlen == 6) {
+				color <<= 8;
+				color |= 0xFF;
+			}
 			sway_log(L_DEBUG, "color: 0x%x", color);
 			break;
+		}
 		case 'i':
 			image_path = optarg;
 			break;