fix(post-with-other-account): put an icon for it

Leaving an empty icon causes the app to crash, which is not fun :(

mastodon/src/main/java/org/joinmastodon/android/ui/utils/UiUtils.java

@@ -1530,7 +1530,7 @@ public static boolean pickAccountForCompose(Activity activity, String accountID)
 
 	public static boolean pickAccountForCompose(Activity activity, String accountID, Bundle args) {
 		if (AccountSessionManager.getInstance().getLoggedInAccounts().size() > 1) {
-			UiUtils.pickAccount(activity, accountID, 0, 0, session -> {
+			UiUtils.pickAccount(activity, accountID, 0, R.drawable.ic_fluent_compose_28_regular, session -> {
 				args.putString("account", session.getID());
 				Nav.go(activity, ComposeFragment.class, args);
 			}, null);

mastodon/src/main/res/drawable/ic_fluent_compose_28_regular.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="28dp"
+    android:height="28dp"
+    android:viewportWidth="28"
+    android:viewportHeight="28">
+  <path
+      android:pathData="M25.78,3.28C26.073,2.987 26.073,2.513 25.78,2.22C25.487,1.927 25.013,1.927 24.72,2.22L11.47,15.47L11.004,17L12.53,16.53L25.78,3.28ZM6.25,3C4.455,3 3,4.455 3,6.25V21.75C3,23.545 4.455,25 6.25,25H21.75C23.545,25 25,23.545 25,21.75V11.205C25,10.79 24.664,10.455 24.25,10.455C23.836,10.455 23.5,10.79 23.5,11.205V21.75C23.5,22.716 22.716,23.5 21.75,23.5H6.25C5.284,23.5 4.5,22.716 4.5,21.75V6.25C4.5,5.284 5.284,4.5 6.25,4.5H16.795C17.21,4.5 17.545,4.164 17.545,3.75C17.545,3.336 17.21,3 16.795,3H6.25Z"
+      android:fillColor="@color/fluent_default_icon_tint"/>
+</vector>