Properly cancel HTTP requests (#6665)
Properly cancel HTTP requests (#6665)

`NetJavaImpl#cancelHttpRequest` cancels pending downloads by canceling the submitted executor service HTTP request task.
Fixes #6664.
tommyettinger/libgdx,NathanSweet/libgdx,libgdx/libgdx,NathanSweet/libgdx,NathanSweet/libgdx,Zomby2D/libgdx,bladecoder/libgdx,stinsonga/libgdx,Zomby2D/libgdx,tommyettinger/libgdx,libgdx/libgdx,stinsonga/libgdx,cypherdare/libgdx,tommyettinger/libgdx,bladecoder/libgdx,libgdx/libgdx,cypherdare/libgdx,bladecoder/libgdx,stinsonga/libgdx,Zomby2D/libgdx,libgdx/libgdx,tommyettinger/libgdx,cypherdare/libgdx,cypherdare/libgdx,stinsonga/libgdx,bladecoder/libgdx,Zomby2D/libgdx,NathanSweet/libgdx,stinsonga/libgdx,libgdx/libgdx,NathanSweet/libgdx,bladecoder/libgdx,tommyettinger/libgdx,Zomby2D/libgdx,cypherdare/libgdx