sd-device: udev-db - handle properties with empty value (#3330)

The statemachine was unable to parse properties with empty values,
reported in [0].

When reaching the start of the KEY, we would unconditionally read
one more character before starting to look for the end-of-line.
Simply look for the end-of-line from the first character.

[0]: <https://bugzilla.redhat.com/show_bug.cgi?id=1338823>

src/libsystemd/sd-device/sd-device.c

@@ -561,7 +561,6 @@ int device_read_uevent_file(sd_device *device) {
 
                         state = VALUE;
 
-                        break;
                 case VALUE:
                         if (strchr(NEWLINE, uevent[i])) {
                                 uevent[i] = '\0';