Correct impl. of HasFlag and ResolveChannel (#966)

HasFlag was checking if any of the flags were set, not the ones
specified, and ResolveChannel was still treating the ChannelPermission
enum as before it was changed to a bitflag.

src/Discord.Net.Core/Utils/Permissions.cs

@@ -80,7 +80,7 @@ namespace Discord
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static bool HasFlag(ulong value, ulong flag) => (value & flag) != 0;
+        private static bool HasFlag(ulong value, ulong flag) => (value & flag) == flag;
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void SetFlag(ref ulong value, ulong flag) => value |= flag;
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -161,10 +161,10 @@ namespace Discord
                     else if (!GetValue(resolvedPermissions, ChannelPermission.SendMessages))
                     {
                         //No send permissions on a text channel removes all send-related permissions
-                        resolvedPermissions &= ~(1UL << (int)ChannelPermission.SendTTSMessages);
-                        resolvedPermissions &= ~(1UL << (int)ChannelPermission.MentionEveryone);
-                        resolvedPermissions &= ~(1UL << (int)ChannelPermission.EmbedLinks);
-                        resolvedPermissions &= ~(1UL << (int)ChannelPermission.AttachFiles);
+                        resolvedPermissions &= ~(ulong)ChannelPermission.SendTTSMessages;
+                        resolvedPermissions &= ~(ulong)ChannelPermission.MentionEveryone;
+                        resolvedPermissions &= ~(ulong)ChannelPermission.EmbedLinks;
+                        resolvedPermissions &= ~(ulong)ChannelPermission.AttachFiles;
                     }
                 }
                 resolvedPermissions &= mask; //Ensure we didnt get any permissions this channel doesnt support (from guildPerms, for example)
@@ -173,4 +173,4 @@ namespace Discord
             return resolvedPermissions;
         }
     }
-}
+}