Fixing of AutoBuffer::allocate(nsz) method

AutoBuffer::allocate(nsz) didn't work properly when
(sz < nsz < fixed_size). In this case sz remained unchanged.

modules/core/include/opencv2/core/utility.hpp

@@ -817,10 +817,10 @@ AutoBuffer<_Tp, fixed_size>::allocate(size_t _size)
         return;
     }
     deallocate();
+    sz = _size;
     if(_size > fixed_size)
     {
         ptr = new _Tp[_size];
-        sz = _size;
     }
 }
 

modules/core/test/test_utils.cpp

@@ -27,6 +27,7 @@ TEST(CommandLineParser, testFailure)
     parser.get<bool>("h");
     EXPECT_FALSE(parser.check());
 }
+
 TEST(CommandLineParser, testHas_noValues)
 {
     const char* argv[] = {"<bin>", "-h", "--info"};
@@ -218,4 +219,17 @@ TEST(CommandLineParser, positional_regression_5074_equal_sign)
     EXPECT_TRUE(parser.check());
 }
 
+
+TEST(AutoBuffer, allocate_test)
+{
+    AutoBuffer<int, 5> abuf(2);
+    EXPECT_EQ(2, abuf.size());
+
+    abuf.allocate(4);
+    EXPECT_EQ(4, abuf.size());
+
+    abuf.allocate(6);
+    EXPECT_EQ(6, abuf.size());
+}
+
 } // namespace