fix: Tax Withholding Category Description default

This commit fixes a bug that happens when a Purchase Invoice uses a
Tax Withholding Category without a category_name. The category_name is
used as the tax description which is a required field. The bug was
fixed by using the Tax Withholding Category's name as the description
if the category_name is empty.
diff --git a/erpnext/accounts/doctype/tax_withholding_category/tax_withholding_category.py b/erpnext/accounts/doctype/tax_withholding_category/tax_withholding_category.py
index dd6b4fd..e904a68 100644
--- a/erpnext/accounts/doctype/tax_withholding_category/tax_withholding_category.py
+++ b/erpnext/accounts/doctype/tax_withholding_category/tax_withholding_category.py
@@ -58,7 +58,7 @@
 				"rate": tax_rate_detail.tax_withholding_rate,
 				"threshold": tax_rate_detail.single_threshold,
 				"cumulative_threshold": tax_rate_detail.cumulative_threshold,
-				"description": tax_withholding.category_name
+				"description": tax_withholding.category_name.strip() if tax_withholding.category_name.strip() else tax_withholding_category
 			})
 
 def get_tax_withholding_rates(tax_withholding, fiscal_year):
@@ -225,4 +225,4 @@
 			certificate_limit > deducted_amount):
 		valid = True
 
-	return valid
\ No newline at end of file
+	return valid