Fix yet another deadlock
Fix yet another deadlock

EventBox.Set should not be called while holding the terminal mutex

  goroutine 1 [semacquire]:
  sync.runtime_SemacquireMutex(0xc0001923bc, 0x1000001066200, 0x1)
          /usr/local/Cellar/go/1.16/libexec/src/runtime/sema.go:71 +0x47
  sync.(*Mutex).lockSlow(0xc0001923b8)
          /usr/local/Cellar/go/1.16/libexec/src/sync/mutex.go:138 +0x105
  sync.(*Mutex).Lock(...)
          /usr/local/Cellar/go/1.16/libexec/src/sync/mutex.go:81
  github.com/junegunn/fzf/src.(*Terminal).Input(0xc000192000, 0x0, 0x0, 0x0, 0x0)
          /fzf/src/terminal.go:581 +0x145
  github.com/junegunn/fzf/src.Run.func10(0xc00010c8a0, 0xc000092050, 0xa)
          /fzf/src/core.go:245 +0x37
  github.com/junegunn/fzf/src.Run.func11(0xc00011a4e0)
          /fzf/src/core.go:295 +0x5ce
  github.com/junegunn/fzf/src/util.(*EventBox).Wait(0xc00011a4e0, 0xc000127ec8)
          /fzf/src/util/eventbox.go:34 +0x5e
  github.com/junegunn/fzf/src.Run(0xc000180000, 0x11ac014, 0x6, 0x11ac158, 0x7)
          /fzf/src/core.go:251 +0xdac
  main.main()
          /fzf/main.go:13 +0x5a

  goroutine 11 [semacquire]:
  sync.runtime_SemacquireMutex(0xc00012c31c, 0xc00010e800, 0x1)
          /usr/local/Cellar/go/1.16/libexec/src/runtime/sema.go:71 +0x47
  sync.(*Mutex).lockSlow(0xc00012c318)
          /usr/local/Cellar/go/1.16/libexec/src/sync/mutex.go:138 +0x105
  sync.(*Mutex).Lock(0xc00012c318)
          /usr/local/Cellar/go/1.16/libexec/src/sync/mutex.go:81 +0x47
  github.com/junegunn/fzf/src/util.(*EventBox).Set(0xc00011a4e0, 0x7, 0x114eb40, 0x1265460)
          /fzf/src/util/eventbox.go:40 +0x3b
  github.com/junegunn/fzf/src.(*Terminal).killPreview(0xc000192000, 0x0)
          /fzf/src/terminal.go:1831 +0xa5
  github.com/junegunn/fzf/src.(*Terminal).exit(0xc000192000, 0xc000106e58)
          /fzf/src/terminal.go:1847 +0x75
  github.com/junegunn/fzf/src.(*Terminal).Loop.func8.1(0xc00011a540)
          /fzf/src/terminal.go:2148 +0x38f
  github.com/junegunn/fzf/src/util.(*EventBox).Wait(0xc00011a540, 0xc000106f90)
          /fzf/src/util/eventbox.go:34 +0x5e
  github.com/junegunn/fzf/src.(*Terminal).Loop.func8(0xc000192000, 0xc00010a2c0)
          /fzf/src/terminal.go:2077 +0xa5
  created by github.com/junegunn/fzf/src.(*Terminal).Loop
          /fzf/src/terminal.go:2072 +0x3e8

junegunn/fzf,junegunn/fzf,junegunn/fzf