Fix duplicate character bug when deleting chars in long strings

If the string is longer than the width of the field and the horizontal
viewport (so to speak) was on the right edge, the last character would
repeat when deleting characters because the viewport offset wasn't being
corrected. This fixes that.

textinput/textinput.go

@@ -135,6 +135,9 @@ func (m *Model) handleOverflow() {
 		return
 	}
 
+	// Correct right offset if we've deleted characters
+	m.offsetRight = min(m.offsetRight, len(m.value))
+
 	if m.pos < m.offset {
 
 		m.offset = m.pos