Fix raw data obs with all flagged tiles being rejected.

These obs should be rejected by default, but if the user wants the input data
tile flags to be ignored, then these obs can be used.

CHANGELOG.md

@@ -26,6 +26,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   (not to be confused with the favoured SHAPELET2 component type).
 - Some MWA raw data observations were not handled correctly due to a
   floating-point error.
+- MWA raw data observations with all flagged tiles weren't allowed to be used,
+  even with the explicit "ignore input data tile flags".
 
 ### Changed
 - The performance of CPU visibility modelling has been dramatically improved.

src/io/read/raw/error.rs

@@ -16,9 +16,6 @@ pub(crate) enum RawReadError {
     #[error("Got a tile flag {got}, but the biggest possible antenna index is {max}!")]
     InvalidTileFlag { got: usize, max: usize },
 
-    #[error("All of this observation's tiles are flagged; cannot continue.")]
-    AllTilesFlagged,
-
     #[error("All of this observation's coarse channels are deemed bad; cannot continue")]
     NoGoodCoarseChannels,
 

src/io/read/raw/mod.rs

@@ -180,7 +180,7 @@ impl RawDataReader {
         let num_unflagged_tiles = total_num_tiles - tile_flags_set.len();
         debug!("There are {} unflagged tiles", num_unflagged_tiles);
         if num_unflagged_tiles == 0 {
-            return Err(RawReadError::AllTilesFlagged);
+            warn!("All of this observation's tiles are flagged");
         }
 
         // Check that the tile flags are sensible.