Limit small message size

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

@@ -2845,11 +2845,11 @@ class Core {
             if (download && message.size != null && !message.ui_hide) {
                 long maxSize;
                 if (state == null || state.networkState.isUnmetered())
-                    maxSize = MessageHelper.DEFAULT_DOWNLOAD_SIZE;
+                    maxSize = MessageHelper.SMALL_MESSAGE_SIZE;
                 else {
                     maxSize = prefs.getInt("download", MessageHelper.DEFAULT_DOWNLOAD_SIZE);
-                    if (maxSize == 0)
+                    if (maxSize == 0 || maxSize > MessageHelper.SMALL_MESSAGE_SIZE)
-                        maxSize = MessageHelper.DEFAULT_DOWNLOAD_SIZE;
+                        maxSize = MessageHelper.SMALL_MESSAGE_SIZE;
                 }
 
                 if (message.size < maxSize) {

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

@@ -113,6 +113,7 @@ public class MessageHelper {
 
     private static File cacheDir = null;
 
+    static final int SMALL_MESSAGE_SIZE = 192 * 1024; // bytes
     static final int DEFAULT_DOWNLOAD_SIZE = 256 * 1024; // bytes
     static final String HEADER_CORRELATION_ID = "X-Correlation-ID";