Possibly fix #2704 "Heltec Wireless Tracker screen doesn't display anything" (#2749)

* fix #2704


Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>

src/main.h

@@ -64,6 +64,8 @@ extern uint32_t shutdownAtMsec;
 
 extern uint32_t serialSinceMsec;
 
+extern int heltec_version;
+
 // If a thread does something that might need for it to be rescheduled ASAP it can set this flag
 // This will suppress the current delay and instead try to run ASAP.
 extern bool runASAP;