qt module: correctly register a found tool and stop looking for it
qt module: correctly register a found tool and stop looking for it

Regression in commit d7ac2f10655433989e5e17867b6c8ef428fd39e8 since
self.{tool_name} is not how it used to be tracked, and the "found"
dictionary is a legacy of the old location.

mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson