crypto: Use getOrPut instead of getOrDefault

getOrDefault won't insert the default value into the map, while we do
want it to be inserted.

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/DefaultCryptoService.kt

@@ -874,7 +874,7 @@ internal class DefaultCryptoService @Inject constructor(
             }
         }
 
-        val keyShareLock = roomKeyShareLocks.getOrDefault(roomId, Mutex())
+        val keyShareLock = roomKeyShareLocks.getOrPut(roomId, { Mutex() })
 
         keyShareLock.withLock {
             coroutineScope {