Fix for some devices that behave strangely with native code.

Sometimes, for whatever reason, native code fails to get installed
on some small percentage of Android devices.  In contrast to every
other device, on LG devices, the call to System.loadLibrary
 *succeeds*, and then the individual native calls throw exceptions.

This change allows the degredation path to work correctly on LG.

android/jni/curve25519-jni.c

@@ -107,3 +107,9 @@ JNIEXPORT jboolean JNICALL Java_org_whispersystems_curve25519_NativeCurve25519Pr
 
     return result;
 }
+
+JNIEXPORT jboolean JNICALL Java_org_whispersystems_curve25519_NativeCurve25519Provider_smokeCheck
+  (JNIEnv *env, jobject obj, jint dummy)
+{
+    return 1;
+}

java/src/main/java/org/whispersystems/curve25519/NativeCurve25519Provider.java

@@ -35,6 +35,12 @@ class NativeCurve25519Provider implements Curve25519Provider {
 
   NativeCurve25519Provider() throws NoSuchProviderException {
     if (!libraryPresent) throw new NoSuchProviderException(libraryFailedException);
+
+    try {
+      smokeCheck(31337);
+    } catch (UnsatisfiedLinkError ule) {
+      throw new NoSuchProviderException(ule);
+    }
   }
 
   @Override
@@ -76,4 +82,6 @@ class NativeCurve25519Provider implements Curve25519Provider {
   @Override
   public native boolean verifySignature(byte[] publicKey, byte[] message, byte[] signature);
 
+  private native boolean smokeCheck(int dummy);
+
 }