[MC-44556] /clear doesn't clear items in armor slot (NPE)

If you try to do /clear while wearing armor, everything except the armor will be cleared, and a NullPointerException will be thrown.

[23:39:59] [Server thread/ERROR]: Couldn't process command
java.lang.NullPointerException
        at yr.a(SourceFile:173) ~[minecraft_server.14w02c.jar:?]
        at ar.b(SourceFile:60) ~[minecraft_server.14w02c.jar:?]
        at y.a(SourceFile:64) [minecraft_server.14w02c.jar:?]
        at np.d(SourceFile:540) [minecraft_server.14w02c.jar:?]
        at np.a(SourceFile:527) [minecraft_server.14w02c.jar:?]
        at iy.a(SourceFile:37) [minecraft_server.14w02c.jar:?]
        at iy.a(SourceFile:9) [minecraft_server.14w02c.jar:?]
        at et.a(SourceFile:166) [minecraft_server.14w02c.jar:?]
        at nk.c(SourceFile:135) [minecraft_server.14w02c.jar:?]
        at net.minecraft.server.MinecraftServer.u(SourceFile:545) [minecraft_server.14w02c.jar:?]
        at mb.u(SourceFile:264) [minecraft_server.14w02c.jar:?]
        at net.minecraft.server.MinecraftServer.t(SourceFile:461) [minecraft_server.14w02c.jar:?]
        at net.minecraft.server.MinecraftServer.run(SourceFile:379) [minecraft_server.14w02c.jar:?]
        at lr.run(SourceFile:647) [minecraft_server.14w02c.jar:?]