fix #68 (@girtsf, pls review - ps: no worries ;-) )

// We don't set useDisplay until setup() is called, because some boards have a declaration of this object but the device
// is never found when probing i2c and therefore we don't call setup and never want to do (invalid) accesses to this device.

src/screen.cpp

@@ -402,7 +402,7 @@ void _screen_header()
 #endif
 
 Screen::Screen(uint8_t address, uint8_t sda, uint8_t scl)
-    : cmdQueue(32), useDisplay(sda || scl), dispdev(address, sda, scl), ui(&dispdev)
+    : cmdQueue(32), useDisplay(false), dispdev(address, sda, scl), ui(&dispdev)
 {
 }
 
@@ -425,8 +425,9 @@ void Screen::handleSetOn(bool on)
 
 void Screen::setup()
 {
-    if (!useDisplay)
-        return;
+    // We don't set useDisplay until setup() is called, because some boards have a declaration of this object but the device
+    // is never found when probing i2c and therefore we don't call setup and never want to do (invalid) accesses to this device.
+    useDisplay = true;
 
     dispdev.resetOrientation();