Changed unconvertable-character symbol to ¿ and made it return only one per unconvertable sequence

src/screen.h

@@ -154,9 +154,11 @@ class Screen : public PeriodicTask
         // UTF-8 to font table index converter
         // Code form http://playground.arduino.cc/Main/Utf8ascii
         static uint8_t LASTCHAR;
+        static bool SKIPREST;   // Only display a single unconvertable-character symbol per sequence of unconvertable characters
 
         if (ch < 128) { // Standard ASCII-set 0..0x7F handling
             LASTCHAR = 0;
+            SKIPREST = false;
             return ch;
         }
 
@@ -164,12 +166,15 @@ class Screen : public PeriodicTask
         LASTCHAR = ch;
 
         switch (last) {    // conversion depnding on first UTF8-character
-            case 0xC2: return (uint8_t) ch;
-            case 0xC3: return (uint8_t) (ch | 0xC0);
-            case 0x82: if (ch == 0xAC) return (uint8_t) 0x80;    // special case Euro-symbol
+            case 0xC2: { SKIPREST = false; return (uint8_t) ch; }
+            case 0xC3: { SKIPREST = false; return (uint8_t) (ch | 0xC0); }
+            case 0x82: { SKIPREST = false; if (ch == 0xAC) return (uint8_t) 0x80; }   // special case Euro-symbol
         }
+        // If we already returned an unconvertable-character symbol for this unconvertable-character sequence, return NULs for the rest of it
+        if (SKIPREST) return (uint8_t) 0;
+        SKIPREST = true;
 
-        return (uint8_t) '?'; // otherwise: return ?, if character can't be converted
+        return (uint8_t) 0xA8; // otherwise: return ¿ if character can't be converted
     }
 
     /// Returns a handle to the DebugInfo screen.