Fixed several issues found by static analysis

modules/imgcodecs/src/bitstrm.cpp

@@ -76,6 +76,7 @@ RBaseStream::RBaseStream()
 {
     m_start = m_end = m_current = 0;
     m_file = 0;
+    m_block_pos = 0;
     m_block_size = BS_DEF_BLOCK_SIZE;
     m_is_opened = false;
     m_allocated = false;

modules/imgcodecs/src/grfmt_exr.cpp

@@ -208,9 +208,12 @@ bool  ExrDecoder::readData( Mat& img )
 
     xstep = m_native_depth ? 4 : 1;
 
+    AutoBuffer<char> copy_buffer;
+
     if( !m_native_depth || (!color && m_iscolor ))
     {
-        buffer = (char *)new float[ m_width * 3 ];
+        copy_buffer.allocate(sizeof(float) * m_width * 3);
+        buffer = copy_buffer;
         ystep = 0;
     }
     else
@@ -388,11 +391,6 @@ bool  ExrDecoder::readData( Mat& img )
 
     close();
 
-    if( !m_native_depth || (!color && m_iscolor ))
-    {
-        delete[] buffer;
-    }
-
     return result;
 }
 

modules/imgcodecs/src/grfmt_jpeg.cpp

@@ -364,7 +364,7 @@ int my_jpeg_load_dht (struct jpeg_decompress_struct *info, unsigned char *dht,
 
        if (index & 0x10)
        {
-           index -= 0x10;
+           index &= ~0x10;
            hufftbl = &ac_tables[index];
        }
        else