Rewritten body part decoding

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

@@ -0,0 +1,24 @@
+package eu.faircode.email;
+
+import java.nio.charset.Charset;
+import java.nio.charset.spi.CharsetProvider;
+import java.util.Collections;
+import java.util.Iterator;
+
+public class UnknownCharsetProvider extends CharsetProvider {
+    @Override
+    public Iterator<Charset> charsets() {
+        return Collections.emptyIterator();
+    }
+
+    @Override
+    public Charset charsetForName(String name) {
+        // x-binaryenc
+        // UseInqueCodePage
+        // none
+        // unknown-8bit
+        // https://javaee.github.io/javamail/FAQ#unsupen
+        Log.w("Unknown charset=" + name);
+        return Charset.forName("US-ASCII");
+    }
+}