Fix v_signmask for RISC-V Vector.

modules/core/include/opencv2/core/hal/intrin_rvv_scalable.hpp

@@ -1618,7 +1618,7 @@ inline int v_signmask(const _Tpvec& a) \
 { \
     uint8_t ans[4] = {0}; \
     vsm(ans, vmslt(a, 0, VTraits<_Tpvec>::vlanes()), VTraits<_Tpvec>::vlanes()); \
-    return *(reinterpret_cast<int*>(ans)); \
+    return *(reinterpret_cast<int*>(ans)) & (((__int128_t)1 << VTraits<_Tpvec>::vlanes()) - 1); \
 } \
 inline int v_scan_forward(const _Tpvec& a) \
 { \

modules/core/test/test_intrin_utils.hpp

@@ -1081,6 +1081,7 @@ template<typename R> struct TheTest
         typedef typename VTraits<uint_reg>::lane_type uint_type;
 
         Data<R> dataA, dataB(0), dataC, dataD(1), dataE(2);
+        dataA[0] = std::numeric_limits<int_type>::max();
         dataA[1] *= (LaneType)-1;
         union
         {