[Excel Analyzer] fix hidden column count

Hidden columns that intersect a blank row would raise an exception:
> NoMethodError: undefined method `[]' for nil:NilClass

gems/excel_analyzer/lib/excel_analyzer/metadata.rb

@@ -49,7 +49,7 @@ def hidden_columns
         end
 
         hidden_columns.count do |c|
-          cells = sheet.sheet_data.rows.map { _1[c - 1] }
+          cells = sheet.sheet_data.rows.compact.map { _1[c - 1] }
           cells.compact.any? { !_1.value.to_s.empty? }
         end
       end

gems/excel_analyzer/spec/excel_analyzer/probe_spec.rb

@@ -5,8 +5,17 @@
 RSpec.describe ExcelAnalyzer::Probe do
   include ExcelAnalyzer::Probe
 
+  def fixture(filename)
+    File.open(File.join(__dir__, "../fixtures/#{filename}"))
+  end
+
   it "does not error if workbook has chartsheets" do
-    xlsx = File.open(File.join(__dir__, "../fixtures/chartsheet.xlsx"))
+    xlsx = fixture("chartsheet.xlsx")
+    expect(probe(xlsx)).to be_a(Hash)
+  end
+
+  it "does not error if workbook has hidden cols that intersect a blank row" do
+    xlsx = fixture("hidden-cols-blank-row.xlsx")
     expect(probe(xlsx)).to be_a(Hash)
   end
 end