fix: make sure there's space for wide characters

`LineBuffer.putString()` did not account for wide characters when adding
text to the buffer.

Author: quintesse

twinkle-ansi/src/main/java/org/codejive/twinkle/util/StyledAppendable.java

@@ -0,0 +1,3 @@
+package org.codejive.twinkle.util;
+
+public interface StyledAppendable extends Appendable {}

twinkle-core/src/main/java/org/codejive/twinkle/core/text/LineBuffer.java

@@ -213,11 +213,16 @@ public int putStringAt(int index, @NonNull StyledIterator iter) {
                 break;
             }
             if (iter.width() == 0) {
-                // We shouldn't be getting any of these from a StyledIterator, but just in case...
+                // Skip any zero-width characters
                 continue;
             }
+            long style = iter.styleState();
+            if (iter.width() == 2 && (cnt + 1) >= len) {
+                // Not enough space for a wide character
+                setCharAt_(startIndex + cnt, style, REPLACEMENT_CHAR);
+                break;
+            }
             if (cnt < len) {
-                long style = iter.styleState();
                 if (iter.isComplex()) {
                     setCharAt_(startIndex + cnt, style, iter.sequence());
                 } else {