fix: Ensure initial status length calculation includes the content warning (#821)

Previous code set `doOnTextChanged` listener for the content warning
*after* the initial value had been set. This meant the initial content
warning text was not included when calculating the status' initial
length.

Fix that by setting the listener before the text is set.

Fixes #815

app/src/main/java/app/pachli/components/compose/ComposeActivity.kt

@@ -396,12 +396,12 @@ class ComposeActivity :
     }
 
     private fun setupContentWarningField(startingContentWarning: String?) {
-        if (startingContentWarning != null) {
-            binding.composeContentWarningField.setText(startingContentWarning)
-        }
         binding.composeContentWarningField.doOnTextChanged { newContentWarning, _, _, _ ->
             viewModel.onContentWarningChanged(newContentWarning?.toString() ?: "")
         }
+        if (startingContentWarning != null) {
+            binding.composeContentWarningField.setText(startingContentWarning)
+        }
     }
 
     private fun setupComposeField(