Fixed crash related to user selection

app/src/main/java/net/novagamestudios/kaffeekasse/ui/login/UserSelection.kt

@@ -323,7 +323,7 @@ private fun UserGridWithSelectionBar(
     )
 
     val onSelectIndex: (Int) -> Unit = block@{ index ->
-        val (userIndex, charIndex) = (userIndexAndCharIndexByChar[chars[index]] ?: return@block)
+        val (userIndex, charIndex) = (userIndexAndCharIndexByChar[chars[index.coerceIn(chars.indices)]] ?: return@block)
         val sectionIndex = userIndex + charIndex
         coroutineScope.launch {
             gridState.scrollToItem(sectionIndex)