Fixed Android 5 signature error

app/src/main/java/eu/faircode/email/EncryptionHelper.java

@@ -20,6 +20,7 @@ package eu.faircode.email;
 */
 
 import android.content.Context;
+import android.os.Build;
 
 import org.bouncycastle.jce.provider.BouncyCastleProvider;
 
@@ -28,19 +29,31 @@ import java.security.Security;
 
 public class EncryptionHelper {
     static {
-        try {
-            Provider[] providers = Security.getProviders();
-            for (int p = 0; p < providers.length; p++)
-                if (BouncyCastleProvider.PROVIDER_NAME.equals(providers[p].getName())) {
-                    Security.removeProvider(BouncyCastleProvider.PROVIDER_NAME);
-                    Provider bc = new BouncyCastleProvider();
-                    Security.insertProviderAt(bc, p + 1);
-                    Log.i("Replacing security provider " + providers[p] + " at " + p + " by " + bc);
-                    break;
-                }
-        } catch (Throwable ex) {
-            Log.e(ex);
-        }
+        /*
+            Caused by: java.lang.SecurityException: Incorrect signature
+              at org.apache.harmony.security.utils.JarUtils.verifySignature(JarUtils.java:223)
+              at java.util.jar.JarVerifier.verifyCertificate(JarVerifier.java:294)
+              at java.util.jar.JarVerifier.readCertificates(JarVerifier.java:268)
+              at java.util.jar.JarFile.getInputStream(JarFile.java:380)
+              at libcore.net.url.JarURLConnectionImpl.getInputStream(JarURLConnectionImpl.java:222)
+              at java.net.URL.openStream(URL.java:470)
+              at java.lang.ClassLoader.getResourceAsStream(ClassLoader.java:444)
+              at java.lang.Class.getResourceAsStream(Class.java:1334)
+         */
+        if (Build.VERSION.SDK_INT > Build.VERSION_CODES.LOLLIPOP_MR1)
+            try {
+                Provider[] providers = Security.getProviders();
+                for (int p = 0; p < providers.length; p++)
+                    if (BouncyCastleProvider.PROVIDER_NAME.equals(providers[p].getName())) {
+                        Security.removeProvider(BouncyCastleProvider.PROVIDER_NAME);
+                        Provider bc = new BouncyCastleProvider();
+                        Security.insertProviderAt(bc, p + 1);
+                        Log.i("Replacing security provider " + providers[p] + " at " + p + " by " + bc);
+                        break;
+                    }
+            } catch (Throwable ex) {
+                Log.e(ex);
+            }
     }
 
     static void init(Context context) {