Fixed a problem that Umlauts where not working in the default FontTableLookup

Author: helmut64

src/OLEDDisplay.cpp

@@ -965,7 +965,7 @@ void OLEDDisplay::setFontTableLookupFunction(FontTableLookupFunction function) {
 }
 
 
-char DefaultFontTableLookup(const char ch) {
+char DefaultFontTableLookup(const uint8_t ch) {
     // UTF-8 to font table index converter
     // Code form http://playground.arduino.cc/Main/Utf8ascii
 	static uint8_t LASTCHAR;

src/OLEDDisplay.h

@@ -141,8 +141,8 @@ enum OLEDDISPLAY_GEOMETRY {
   GEOMETRY_RAWMODE,
 };
 
-typedef char (*FontTableLookupFunction)(const char ch);
-char DefaultFontTableLookup(const char ch);
+typedef char (*FontTableLookupFunction)(const uint8_t ch);
+char DefaultFontTableLookup(const uint8_t ch);
 
 
 #ifdef ARDUINO