handle null emojify inputs better

fixes #3889
Closes #3901
// FREEBIE

src/org/thoughtcrime/securesms/components/emoji/EmojiFilter.java

@@ -19,7 +19,7 @@ public class EmojiFilter implements InputFilter {
     char[] v = new char[end - start];
     TextUtils.getChars(source, start, end, v, 0);
     Spannable emojified = EmojiProvider.getInstance(view.getContext()).emojify(new String(v), view);
-    if (source instanceof Spanned) {
+    if (source instanceof Spanned && emojified != null) {
       TextUtils.copySpansFrom((Spanned) source, start, end, null, emojified, 0);
     }
     return emojified;

src/org/thoughtcrime/securesms/components/emoji/EmojiProvider.java

@@ -12,6 +12,8 @@ import android.graphics.drawable.Drawable;
 import android.os.AsyncTask;
 import android.os.Build.VERSION;
 import android.os.Build.VERSION_CODES;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.text.Spannable;
 import android.text.SpannableStringBuilder;
 import android.util.Log;
@@ -78,7 +80,8 @@ public class EmojiProvider {
     }
   }
 
-  public Spannable emojify(CharSequence text, TextView tv) {
+  public @Nullable Spannable emojify(@Nullable CharSequence text, @NonNull TextView tv) {
+    if (text == null) return null;
     Matcher                matches = EMOJI_RANGE.matcher(text);
     SpannableStringBuilder builder = new SpannableStringBuilder(text);
 

src/org/thoughtcrime/securesms/components/emoji/EmojiTextView.java

@@ -4,6 +4,7 @@ import android.content.Context;
 import android.graphics.Paint.FontMetricsInt;
 import android.graphics.drawable.Drawable;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.widget.AppCompatTextView;
 import android.text.TextUtils;
 import android.text.TextUtils.TruncateAt;
@@ -28,12 +29,12 @@ public class EmojiTextView extends AppCompatTextView {
     super(context, attrs, defStyleAttr);
   }
 
-  @Override public void setText(CharSequence text, BufferType type) {
+  @Override public void setText(@Nullable CharSequence text, BufferType type) {
     source = EmojiProvider.getInstance(getContext()).emojify(text, this);
     setTextEllipsized(source);
   }
 
-  public void setTextEllipsized(final CharSequence source) {
+  public void setTextEllipsized(final @Nullable CharSequence source) {
     super.setText(needsEllipsizing ? ViewUtil.ellipsize(source, this) : source, BufferType.SPANNABLE);
   }