fix: raise ValueError when iHS/XP-EHH arrays are empty after filtering

Signed-off-by: Suhrid Marwah <suhridmarwah07@gmail.com>

Author: suhr25

malariagen_data/anopheles.py

@@ -970,6 +970,12 @@ def plot_ihs_gwss_track(
             inline_array=inline_array,
         )
 
+        if len(x) == 0:
+            raise ValueError(
+                "No iHS values remain after filtering. "
+                "Try relaxing filter_min_maf or min_ehh parameters."
+            )
+
         # determine X axis range
         x_min = x[0]
         x_max = x[-1]
@@ -1494,6 +1500,12 @@ def plot_xpehh_gwss_track(
             inline_array=inline_array,
         )
 
+        if len(x) == 0:
+            raise ValueError(
+                "No XP-EHH values remain after filtering. "
+                "Try relaxing filter_min_maf or min_ehh parameters."
+            )
+
         # determine X axis range
         x_min = x[0]
         x_max = x[-1]