Prevent crash

app/src/main/java/eu/faircode/email/ActivitySignature.java

@@ -197,6 +197,8 @@ public class ActivitySignature extends ActivityBase {
             etText.setText(HtmlHelper.fromHtml(html, new Html.ImageGetter() {
                 @Override
                 public Drawable getDrawable(String source) {
+                    if (source != null && source.startsWith("cid:"))
+                        source = null;
                     return ImageHelper.decodeImage(ActivitySignature.this, -1, source, true, 0, 1.0f, etText);
                 }
             }, null, this));

app/src/main/java/eu/faircode/email/FragmentAnswer.java

@@ -196,6 +196,8 @@ public class FragmentAnswer extends FragmentBase {
                         etText.setText(HtmlHelper.fromHtml(answer.text, new Html.ImageGetter() {
                             @Override
                             public Drawable getDrawable(String source) {
+                                if (source != null && source.startsWith("cid:"))
+                                    source = null;
                                 return ImageHelper.decodeImage(getContext(), -1, source, true, 0, 1.0f, etText);
                             }
                         }, null, getContext()));

app/src/main/java/eu/faircode/email/FragmentCompose.java

@@ -1647,6 +1647,8 @@ public class FragmentCompose extends FragmentBase {
                                 Spanned spanned = HtmlHelper.fromHtml(html, new Html.ImageGetter() {
                                     @Override
                                     public Drawable getDrawable(String source) {
+                                        if (source != null && source.startsWith("cid:"))
+                                            source = null;
                                         return ImageHelper.decodeImage(getContext(), working, source, true, zoom, 1.0f, etBody);
                                     }
                                 }, null, getContext());