Merge pull request opencv#25864 from vrabaud:legacy

Make sure all the lines of a JPEG are read opencv#25864

In case of corrupted JPEG, imread would still return a JPEG of the proper size (as indicated by the header) but with some uninitialized values. I do not have a short reproducer I can add as a test as this was found by our fuzzers.

### Pull Request Readiness Checklist

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- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
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modules/imgcodecs/src/grfmt_jpeg.cpp

@@ -499,7 +499,7 @@ bool  JpegDecoder::readData( Mat& img )
                 for( int iy = 0 ; iy < m_height; iy ++ )
                 {
                     uchar* data = img.ptr<uchar>(iy);
-                    jpeg_read_scanlines( cinfo, &data, 1 );
+                    if (jpeg_read_scanlines( cinfo, &data, 1 ) != 1) return false;
                 }
             }
             else
@@ -510,7 +510,7 @@ bool  JpegDecoder::readData( Mat& img )
                 for( int iy = 0 ; iy < m_height; iy ++ )
                 {
                     uchar* data = img.ptr<uchar>(iy);
-                    jpeg_read_scanlines( cinfo, buffer, 1 );
+                    if (jpeg_read_scanlines( cinfo, buffer, 1 ) != 1) return false;
 
                     if( color )
                     {