fix findmin/findmax with nan (#722)

Closes #714

Author: araujoms

src/sparsevector.jl

@@ -1704,7 +1704,7 @@ for (fun, comp, word) in ((:findmin, :(<), "minimum"), (:findmax, :(>), "maximum
         m == n && return val, index
         nzinds = nonzeroinds(x)
         zeroval = f(zero(T))
-        $comp(val, zeroval) && return val, nzinds[index]
+        ($comp(val, zeroval) || isnan(val)) && return val, nzinds[index]
         # we need to find the first zero, which could be stored or implicit
         # we try to avoid findfirst(iszero, x)
         sindex = findfirst(_iszero, nzvals) # first stored zero, if any

test/sparsevector.jl

@@ -1052,6 +1052,11 @@ end
         @test all(!iszero, v)
         @test !any(iszero, v)
     end
+
+    let v = sparse([0, NaN]) #issue #714
+        @test findmin(v) === (NaN, 2)
+        @test findmax(v) === (NaN, 2)
+    end
 end
 
 ### linalg