Throw error with invalid network with fromString

lib/address.js

@@ -195,10 +195,14 @@ Address._transformBuffer = function(buffer, network, type) {
     throw new TypeError('Address buffers must be exactly 21 bytes.');
   }
 
-  network = Networks.get(network);
+  var networkObj = Networks.get(network);
   var bufferVersion = Address._classifyFromVersion(buffer);
 
-  if (!bufferVersion.network || (network && network !== bufferVersion.network)) {
+  if (network && !networkObj) {
+    throw new TypeError('Unknown network');
+  }
+
+  if (!bufferVersion.network || (networkObj && networkObj !== bufferVersion.network)) {
     throw new TypeError('Address has mismatched network type.');
   }
 

test/address.js

@@ -250,6 +250,12 @@ describe('Address', function() {
       Address.fromString(str, Networks.livenet).toString().should.equal(str);
     });
 
+    it('should throw with bad network param', function() {
+      (function(){
+        Address.fromString(str, 'somenet');
+      }).should.throw('Unknown network');
+    });
+
     it('should error because of unrecognized data format', function() {
       (function() {
         return new Address(new Error());

test/networks.js

@@ -89,7 +89,10 @@ describe('Networks', function() {
     networks.add(custom);
     var network = networks.get(undefined);
     should.not.exist(network);
-    networks.remove(custom);
+    var somenet = networks.get('somenet');
+    should.exist(somenet);
+    somenet.name.should.equal('somenet');
+    networks.remove(somenet);
   });
 
   var constants = ['name', 'alias', 'pubkeyhash', 'scripthash', 'xpubkey', 'xprivkey'];