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;
 
@@ -28,6 +29,18 @@ import java.security.Security;
 
 public class EncryptionHelper {
     static {
+        /*
+            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++)