Fix usingCancellable with null ret value

app/src/main/java/com/hippo/ehviewer/client/EhEngine.kt

@@ -116,7 +116,7 @@ private fun rethrowExactly(code: Int, headers: Headers, body: String, e: Throwab
     throw e
 }
 
-private suspend inline fun <T> Request.executeAndParsingWith(block: String.() -> T): T {
+private suspend inline fun <T> Request.executeAndParsingWith(crossinline block: String.() -> T): T {
     Log.d(TAG, url.toString())
     return execute {
         val body = body.string()

app/src/main/java/com/hippo/ehviewer/client/EhRequestBuilder.kt

@@ -79,10 +79,11 @@ suspend inline fun <R> Call.usingCancellable(crossinline block: Response.() -> R
                     r.exceptionOrNull()?.let {
                         Log.e(TAG_CALL, "Reading response of call$call failed!")
                         cont.resumeWithException(it)
-                    }
-                    r.getOrNull()?.let {
+                    } ?: run {
                         Log.d(TAG_CALL, "Reading response of call$call succeed!")
-                        cont.resume(it)
+                        // R maybe null
+                        @Suppress("UNCHECKED_CAST")
+                        cont.resume(r.getOrNull() as R)
                     }
                 } else if (isCanceled() && cont.isActive) {
                     Log.e(TAG_CALL, "call$call cancelled but coroutine is Active!")