Small fixes

Author: Rylern

src/main/java/qupath/ext/align/core/AutoAligner.java

@@ -253,8 +253,11 @@ private static AffineTransform alignWithPoints(
                     case AFFINE -> opencv_calib3d.estimateAffine2D(baseMat, matToAlign);
                     case RIGID -> opencv_calib3d.estimateAffinePartial2D(baseMat, matToAlign);
                 };
-                Indexer indexer = matTransform.createIndexer()
+                Indexer indexer = matTransform.ptr() == null ? null : matTransform.createIndexer()
         ) {
+            if (indexer == null) {
+                throw new NullPointerException("Failed to estimate the transformation.");
+            }
             return matToTransform(indexer, 1.0);
         }
     }

src/test/java/qupath/ext/align/core/TestAutoAligner.java

@@ -149,7 +149,7 @@ void Check_Intensity_Auto_Alignment_On_Translated_Image_With_Downsample(AutoAlig
                 downsample
         );
 
-        assertAffineAlmostEquals(expectedTransform, transform, .2);
+        assertAffineAlmostEquals(expectedTransform, transform, .5);
 
         baseImageData.close();
         baseServer.close();