rtc: fix setting time from driftfile when RTC reading fails

Fix RTC_Linux_TimePreInit() to return 0 when the RTC device can be
opened, but reading its time fails to at least have the time restored
from the driftfile.

rtc_linux.c

@@ -1051,6 +1051,8 @@ RTC_Linux_TimePreInit(void)
       LOG(LOGS_WARN, LOGF_RtcLinux, "Could not convert RTC reading to seconds since 1/1/1970");
       return 0;
     }
+  } else {
+    return 0;
   }
 
   return 1;