fix(util/lean_path): clear g_lean_path_vector before (re-)initializing it
fix(util/lean_path): clear g_lean_path_vector before (re-)initializing it

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

leodemoura/lean,digama0/lean,fgdorais/lean,Kha/lean,avigad/lean,htzh/lean,soonhokong/lean-osx,sp3ctum/lean,rlewis1988/lean,johoelzl/lean,leodemoura/lean,digama0/lean,UlrikBuchholtz/lean,fpvandoorn/lean2,sp3ctum/lean,htzh/lean,dselsam/lean,fgdorais/lean,fgdorais/lean,Kha/lean,leanprover-community/lean,fgdorais/lean,levnach/lean,leanprover-community/lean,htzh/lean,UlrikBuchholtz/lean,avigad/lean,leanprover/lean,avigad/lean,leanprover/lean,eigengrau/lean,johoelzl/lean,eigengrau/lean,leanprover/lean,johoelzl/lean,javra/lean,fpvandoorn/lean,soonhokong/lean,rlewis1988/lean,dselsam/lean,Kha/lean,soonhokong/lean-windows,soonhokong/lean-windows,Kha/lean,c-cube/lean,avigad/lean,soonhokong/lean,soonhokong/lean-windows,fpvandoorn/lean2,levnach/lean,soonhokong/lean-windows,leanprover/lean,htzh/lean,leanprover-community/lean,fpvandoorn/lean,dselsam/lean,c-cube/lean,sp3ctum/lean,soonhokong/lean,soonhokong/lean-osx,leodemoura/lean,fpvandoorn/lean2,javra/lean,dselsam/lean,leodemoura/lean,eigengrau/lean,rlewis1988/lean,htzh/lean,levnach/lean,fpvandoorn/lean,sp3ctum/lean,fgdorais/lean,sp3ctum/lean,UlrikBuchholtz/lean,leanprover-community/lean,leanprover-community/lean,soonhokong/lean,levnach/lean,dselsam/lean,leanprover/lean,soonhokong/lean-windows,soonhokong/lean-osx,avigad/lean,soonhokong/lean-osx,Kha/lean,fpvandoorn/lean,digama0/lean,leanprover/lean,digama0/lean,c-cube/lean,leodemoura/lean,rlewis1988/lean,c-cube/lean,soonhokong/lean,UlrikBuchholtz/lean,javra/lean,johoelzl/lean,johoelzl/lean,soonhokong/lean-osx,rlewis1988/lean,eigengrau/lean,UlrikBuchholtz/lean,javra/lean,dselsam/lean,rlewis1988/lean,avigad/lean,johoelzl/lean,c-cube/lean,fgdorais/lean,digama0/lean,leanprover-community/lean,leodemoura/lean,javra/lean,fpvandoorn/lean2,eigengrau/lean,fpvandoorn/lean,levnach/lean,digama0/lean,fpvandoorn/lean,Kha/lean,fpvandoorn/lean2