More palette index checks to avoid getting into a derpy state.

src/main/scala/li/cil/oc/util/PackedColor.scala

@@ -36,6 +36,12 @@ object PackedColor {
 
     def inflate(value: Int): Int
 
+    def validate(value: Color) {
+      if (value.isPalette) {
+        throw new IllegalArgumentException("color palette not supported")
+      }
+    }
+
     def deflate(value: Color): Byte
 
     override def load(nbt: NBTTagCompound) {}
@@ -48,12 +54,20 @@ object PackedColor {
 
     override def inflate(value: Int) = if (value == 0) 0x000000 else 0xFFFFFF
 
-    override def deflate(value: Color) = (if (value.value == 0) 0 else 1).toByte
+    override def deflate(value: Color) = {
+      (if (value.value == 0) 0 else 1).toByte
+    }
   }
 
   abstract class PaletteFormat extends ColorFormat {
     override def inflate(value: Int) = palette(math.max(0, math.min(palette.length - 1, value)))
 
+    override def validate(value: Color) {
+      if (value.isPalette && (value.value < 0 || value.value >= palette.length)) {
+        throw new IllegalArgumentException("invalid palette index")
+      }
+    }
+
     override def deflate(value: Color) =
       if (value.isPalette) (math.max(0, value.value) % palette.length).toByte
       else palette.map(delta(value.value, _)).zipWithIndex.minBy(_._1)._2.toByte

src/main/scala/li/cil/oc/util/TextBuffer.scala

@@ -26,15 +26,19 @@ class TextBuffer(var width: Int, var height: Int, initialFormat: PackedColor.Col
   def foreground = _foreground
 
   def foreground_=(value: PackedColor.Color) = {
+    format.validate(value)
     _foreground = value
     packed = PackedColor.pack(_foreground, _background, _format)
+    this
   }
 
   def background = _background
 
   def background_=(value: PackedColor.Color) = {
+    format.validate(value)
     _background = value
     packed = PackedColor.pack(_foreground, _background, _format)
+    this
   }
 
   def format = _format