Fixed build with libpng older than 1.5.x

modules/imgcodecs/test/test_exif.cpp

@@ -452,7 +452,7 @@ TEST(Imgcodecs_Png, Read_Write_With_Exif)
     EXPECT_EQ(img2.rows, img.rows);
     EXPECT_EQ(img2.type(), imgtype);
     EXPECT_EQ(read_metadata_types, read_metadata_types2);
-    EXPECT_GE(read_metadata_types.size(), 1u);
+    ASSERT_GE(read_metadata_types.size(), 1u);
     EXPECT_EQ(read_metadata, read_metadata2);
     EXPECT_EQ(read_metadata_types[0], IMAGE_METADATA_EXIF);
     EXPECT_EQ(read_metadata_types.size(), read_metadata.size());

modules/imgcodecs/test/test_png.cpp

@@ -19,7 +19,9 @@ TEST(Imgcodecs_Png, write_big)
     EXPECT_EQ(13917, img.rows);
 
     vector<uchar> buff;
-    ASSERT_NO_THROW(imencode(".png", img, buff, { IMWRITE_PNG_ZLIBBUFFER_SIZE, INT_MAX }));
+    bool status = false;
+    ASSERT_NO_THROW(status = imencode(".png", img, buff, { IMWRITE_PNG_ZLIBBUFFER_SIZE, 1024*1024 }));
+    ASSERT_TRUE(status);
 #ifdef HAVE_PNG
     EXPECT_EQ((size_t)816219, buff.size());
 #else
@@ -34,7 +36,9 @@ TEST(Imgcodecs_Png, encode)
     vector<int> param;
     param.push_back(IMWRITE_PNG_COMPRESSION);
     param.push_back(3); //default(3) 0-9.
-    EXPECT_NO_THROW(imencode(".png", img_gt, buff, param));
+    bool status = false;
+    EXPECT_NO_THROW(status = imencode(".png", img_gt, buff, param));
+    ASSERT_TRUE(status);
     Mat img;
     EXPECT_NO_THROW(img = imdecode(buff, IMREAD_ANYDEPTH)); // hang
     EXPECT_FALSE(img.empty());