decoder+mcu_prog: Check for invalid component dimensions.

Makes #8 (comment) correctly panic.

src/decoder.rs

@@ -624,7 +624,7 @@ impl Decoder
     /// before trying to decode.
     pub(crate) fn check_component_dimensions(&self) -> Result<(), DecodeErrors>
     {
-        // find  y component
+       // find  y component
         let y_comp = self
             .components
             .iter()
@@ -646,6 +646,9 @@ impl Decoder
             {
                 return Err(DecodeErrors::Format(format!("Invalid image width and height stride for component {:?}, expected {}, but found {}", comp.component_id, cb_cr_width, comp.width_stride)));
             }
+            if (comp.horizontal_sample != 1 || comp.vertical_sample != 1) && comp.component_id != ComponentID::Y {
+                return Err(DecodeErrors::Format(format!("Invalid component ID for {} for {:?} component, expected 1", comp.horizontal_sample,comp.component_id)));
+            }
         }
 
         Ok(())

src/mcu_prog.rs

@@ -257,6 +257,7 @@ impl Decoder
         &mut self, reader: &mut Cursor<Vec<u8>>, stream: &mut BitStream, buffer: &mut [Vec<i16>; 3],
     ) -> Result<bool, DecodeErrors>
     {
+        self.check_component_dimensions()?;
         stream.reset();
         self.components.iter_mut().for_each(|x| x.dc_pred = 0);
 
@@ -301,6 +302,7 @@ impl Decoder
                     if i >= mcu_height{
                         break;
                     }
+
                     let data: &mut [i16; 64] = buffer.get_mut(k)
                         .unwrap().get_mut(start..start + 64)
                         .unwrap().try_into().unwrap();