fix: RequestBuilder.submitAsync() throwing an Exception if the Glide request is restarted (#4569)

This is the third attempt to fix `RequestBuilder.submitAsync()`. For the
rationale, see the comments of #4436.

We now clear the continuation reference after resuming it, to make sure
that:
1) It will only be resumed once
2) It will not leak the coroutine when Glide keeps the `Request` around.

app/src/main/java/com/keylesspalace/tusky/util/GlideExtensions.kt

@@ -5,6 +5,7 @@ import com.bumptech.glide.load.DataSource
 import com.bumptech.glide.load.engine.GlideException
 import com.bumptech.glide.request.RequestListener
 import com.bumptech.glide.request.target.Target
+import kotlin.coroutines.Continuation
 import kotlin.coroutines.resume
 import kotlin.coroutines.resumeWithException
 import kotlinx.coroutines.suspendCancellableCoroutine
@@ -17,15 +18,25 @@ suspend fun <R> RequestBuilder<R>.submitAsync(
     height: Int = Target.SIZE_ORIGINAL
 ): R {
     return suspendCancellableCoroutine { continuation ->
-        val target = addListener(
+        val target = addListener(ContinuationRequestListener(continuation))
-            object : RequestListener<R> {
+            .submit(width, height)
+        continuation.invokeOnCancellation { target.cancel(true) }
+    }
+}
+
+private class ContinuationRequestListener<R>(continuation: Continuation<R>) : RequestListener<R> {
+    private var continuation: Continuation<R>? = continuation
+
     override fun onLoadFailed(
         e: GlideException?,
         model: Any?,
         target: Target<R>,
         isFirstResource: Boolean
     ): Boolean {
-                    continuation.resumeWithException(e ?: GlideException("Image loading failed"))
+        continuation?.let {
+            continuation = null
+            it.resumeWithException(e ?: GlideException("Image loading failed"))
+        }
         return false
     }
 
@@ -36,13 +47,12 @@ suspend fun <R> RequestBuilder<R>.submitAsync(
         dataSource: DataSource,
         isFirstResource: Boolean
     ): Boolean {
+        continuation?.let {
             if (target?.request?.isComplete == true) {
-                        continuation.resume(resource)
+                continuation = null
+                it.resume(resource)
+            }
         }
         return false
     }
 }
-        ).submit(width, height)
-        continuation.invokeOnCancellation { target.cancel(true) }
-    }
-}