[lcd] forbid writing outside of current framebuffer memory

Current implementation contains full support for:
- transparent switching between direct and framebuffer rendering modes
- writing characters to framebuffers
- loading frame from memory to physical display

As well as partial support for instruction writes including:
- resetting the display (clears memory, sets cursor at 0:0, switches to increment mode)
- switching between increment/decrement modes
- setting cursor position

Core/Src/PCA9685.c

@@ -40,6 +40,8 @@ int PCA9685_run_test(void)
 				display_write_data_seq("/5 ");
 
 				switch (op_result) {
+				case HAL_OK:
+					break;
 				case HAL_ERROR:
 					display_write_data_seq("ERROR");
 					break;

Core/Src/lcd.c

@@ -136,6 +136,12 @@ static void display_write_data_byte_direct(uint8_t code)
 
 static void display_write_data_byte_framebuffer(uint8_t code)
 {
+	if (display_current_frame >= DISPLAY_FRAMES_AVAILABLE)
+		return;
+
+	if (((int) des.cursor_offset >= 32) || ((int) des.cursor_offset < 0))
+		return;
+
 	display_framebuffer[16*2*display_current_frame + des.cursor_offset] = (char) code;
 	des.cursor_offset += des.next ? -1 : 1;
 }