fix: Setup compose button when creating MainActivity (#589)

The compose button isn't initially working on `MainActivity`. It is only
properly setup after changing tabs.

Fix by calling `MainActivity.refreshComposeButtonState(TabViewData)` on
creation.

app/src/main/java/app/pachli/MainActivity.kt

@@ -962,11 +962,13 @@ class MainActivity : BottomSheetActivity(), ActionButtonActivity, MenuProvider {
             activeTabLayout.addOnTabSelectedListener(it)
         }
 
-        supportActionBar?.title = tabs[position].title(this@MainActivity)
+        binding.mainToolbar.title = tabs[position].title(this@MainActivity)
         binding.mainToolbar.setOnClickListener {
             (tabAdapter.getFragment(activeTabLayout.selectedTabPosition) as? ReselectableFragment)?.onReselect()
         }
 
+        refreshComposeButtonState(tabs[position])
+
         updateProfiles()
     }