Fix more compiler warnings

Fixes the following warnings when compiling using GCC 5.4:

    CXX OLEDDisplayUi.o
    ./OLEDDisplayUi.cpp: In member function 'void OLEDDisplayUi::drawFrame()':
    ./OLEDDisplayUi.cpp:284:48: error: 'y1' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
						    ^
    ./OLEDDisplayUi.cpp:284:37: error: 'x1' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
					 ^
    ./OLEDDisplayUi.cpp:284:26: error: 'y' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
			      ^
    ./OLEDDisplayUi.cpp:284:16: error: 'x' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
		    ^
    ./OLEDDisplayUi.cpp: In member function 'void OLEDDisplayUi::drawIndicator()':
    ./OLEDDisplayUi.cpp:393:35: error: 'y' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	   this->display->drawFastImage(x, y, 8, 8, image);
				       ^
    ./OLEDDisplayUi.cpp:393:35: error: 'x' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    ./OLEDDisplayUi.cpp:387:7: error: 'posOfHighlightFrame' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	   if (posOfHighlightFrame == i) {
	   ^
    cc1plus: some warnings being treated as errors

OLEDDisplayUi.cpp

@@ -272,6 +272,7 @@ void OLEDDisplayUi::drawFrame(){
           y1 = y + 64;
           break;
         case SLIDE_DOWN:
+        default:
           x = 0;
           y = 64 * progress;
           x1 = 0;
@@ -345,6 +346,7 @@ void OLEDDisplayUi::drawIndicator() {
         posOfHighlightFrame = frameToHighlight;
         break;
       case RIGHT_LEFT:
+      default:
         posOfHighlightFrame = this->frameCount - frameToHighlight;
         break;
     }
@@ -379,6 +381,7 @@ void OLEDDisplayUi::drawIndicator() {
           y = 32 - frameStartPos + 2 + 12 * i;
           break;
         case LEFT:
+        default:
           x = 0 - (8 * indicatorFadeProgress);
           y = 32 - frameStartPos + 2 + 12 * i;
           break;