fix: Parse.setServer doesn't properly validate URL (#1844)

Author: dplewis

Parse/Parse.xcodeproj/xcshareddata/xcschemes/Parse-iOS.xcscheme

@@ -96,9 +96,6 @@
                <Test
                   Identifier = "ParseClientConfigurationTests/testExtensionDataSharing">
                </Test>
-               <Test
-                  Identifier = "ParseClientConfigurationTests/testServerValidation">
-               </Test>
             </SkippedTests>
          </TestableReference>
       </Testables>

Parse/Parse/Source/ParseClientConfiguration.m

@@ -69,8 +69,9 @@ - (void)setClientKey:(NSString *)clientKey {
 }
 
 - (void)setServer:(NSString *)server {
+    NSURL *url = [NSURL URLWithString:server];
     PFParameterAssert(server.length, @"Server should not be `nil`.");
-    PFParameterAssert([NSURL URLWithString:server], @"Server should be a valid URL.");
+    PFParameterAssert(url && url.scheme && url.host, @"Server should be a valid URL.");
     _server = [server copy];
 }