use SIGHUP for reopening log file

src/ebusd/main.cpp

@@ -590,6 +590,10 @@ void signalHandler(int sig) {
   switch (sig) {
   case SIGHUP:
     logNotice(lf_main, "SIGHUP received");
+    if (!opt.foreground) {
+      closeLogFile();
+      setLogFile(opt.logFile);
+    }
     break;
   case SIGINT:
     logNotice(lf_main, "SIGINT received");

src/lib/utils/log.cpp

@@ -141,6 +141,9 @@ bool needsLog(const LogFacility facility, const LogLevel level) {
 }
 
 void logWrite(const char* facility, const char* level, const char* message, va_list ap) {
+  if (s_logFile == NULL) {
+    return;
+  }
   struct timespec ts;
   struct tm td;
   clockGettime(&ts);