core: parallel_for_(): update RNG state of the main thread

modules/core/include/opencv2/core.hpp

@@ -2834,6 +2834,8 @@ public:
     double gaussian(double sigma);
 
     uint64 state;
+
+    bool operator ==(const RNG& other) const;
 };
 
 /** @brief Mersenne Twister random number generator

modules/core/include/opencv2/core/operations.hpp

@@ -349,6 +349,8 @@ inline int    RNG::uniform(int a, int b)       { return a == b ? a : (int)(next(
 inline float  RNG::uniform(float a, float b)   { return ((float)*this)*(b - a) + a; }
 inline double RNG::uniform(double a, double b) { return ((double)*this)*(b - a) + a; }
 
+inline bool RNG::operator ==(const RNG& other) const { return state == other.state; }
+
 inline unsigned RNG::next()
 {
     state = (uint64)(unsigned)state* /*CV_RNG_COEFF*/ 4164903690U + (unsigned)(state >> 32);