lisp/*.el, src/*.c: Doc fixes related to returning t vs non-nil

lisp/*.el, src/*.c: Doc fixes related to returning t vs non-nil

* lisp/progmodes/flymake-proc.el (flymake-proc--find-buffer-for-file):
Doc fix; return value is a buffer, not t.

* lisp/progmodes/ebrowse.el (ebrowse-member-display-p):
Doc fix; return value is the MEMBER argument, not nil.

* lisp/files.el (hack-one-local-variable-eval-safep):
* lisp/play/doctor.el (doctor-nounp, doctor-pronounp):
* lisp/progmodes/flymake-proc.el (flymake-proc--check-include):
* lisp/progmodes/js.el (js--broken-arrow-terminates-line-p):
Doc fix; a non-nil return value is not always t.

* lisp/image.el (image-type-available-p):
* lisp/simple.el (region-active-p):
* lisp/window.el (frame-root-window-p):
* src/buffer.c (Fbuffer_live_p):
* src/image.c (Finit_image_library):
* src/window.c (Fwindow_minibuffer_p):
Doc fix; a non-nil return value is always t.

* doc/lispref/minibuf.texi (Minibuffer Windows): Doc fix.