Fix coloring of multiline BitmapText

BitmapText internally stores characters with newlines removed, since they don't
need to be rendered. Due to this, BitmapText::AddAttributes() needs to
recalculate attribute positions and lengths in order to apply them in the
correct place. Unfortuantely the code would calculate the position incorrectly
and completely ignore length. Fix it so that everything is correct even in
multiline text.

src/BitmapText.cpp

@@ -879,18 +879,39 @@ BitmapText::Attribute BitmapText::GetDefaultAttribute() const
 void BitmapText::AddAttribute( std::size_t iPos, const Attribute &attr )
 {
 	// Fixup position for new lines.
+	Attribute newAttr = attr;
+	std::vector<std::wstring>::const_iterator lineIter = m_wTextLines.cbegin();
+
 	int iLines = 0;
 	std::size_t iAdjustedPos = iPos;
 
-	for (std::wstring const & line : m_wTextLines)
+	for( ; lineIter != m_wTextLines.cend(); ++lineIter )
 	{
-		std::size_t length = line.length();
-		if( length >= iAdjustedPos )
+		std::size_t length = lineIter->length() + 1; // +1 to account for implicit newline at the end
+		if( length > iAdjustedPos )
 			break;
 		iAdjustedPos -= length;
 		++iLines;
 	}
-	m_mAttributes[iPos-iLines] = attr;
+
+	if( newAttr.length > 0 )
+	{
+		// Fixup length for new lines.
+		std::size_t iAdjustedEndPos = iAdjustedPos + newAttr.length;
+		for( ; lineIter != m_wTextLines.cend(); ++lineIter )
+		{
+			std::size_t length = lineIter->length() + 1; // +1 to account for implicit newline at the end
+			if( length > iAdjustedEndPos || newAttr.length == 0 )
+				break;
+			iAdjustedEndPos -= length;
+			newAttr.length -= 1;
+		}
+	}
+
+	if( newAttr.length == 0 ) // Attribute doesn't cover any printable characters
+		return;
+
+	m_mAttributes[iPos-iLines] = newAttr;
 	m_bHasGlowAttribute = m_bHasGlowAttribute || attr.glow.a > 0.0001f;
 }