Support missing fonts and <dimension> tags

[SGrondin]

Hi, thank you for making and maintaining saxlsx, it's a wonderful library.

I've recently encountered an XLSX file that Excel, LibreOffice, Numbers and the Creek library were able to handle correctly, but not saxlsx. The file itself is incorrect, and it would be great if saxlsx was able to tolerate these small errors.

There were 2 issues, this PR fixes both and includes a test XLSX that contains both errors.

Missing fonts

In xl/styles.xml:

<cellXfs count="3">
  <xf applyBorder="1" applyFill="1" applyFont="1" borderId="0" fillId="0" fontId="1" numFmtId="0"/>
  <xf applyAlignment="1" applyBorder="1" applyFill="1" applyFont="1" applyNumberFormat="1" borderId="0" fillId="0" fontId="2">
    <alignment horizontal="left" readingOrder="1" textRotation="0" vertical="top" wrapText="1"/>
  </xf>
  <xf applyAlignment="1" applyBorder="1" applyFill="1" applyFont="1" applyNumberFormat="1" borderId="0" fillId="0" fontId="2" numFmtId="82">
    <alignment horizontal="left" readingOrder="1" textRotation="0" vertical="top" wrapText="1"/>
  </xf>
</cellXfs>

Notice how one of the <xf> tags is missing numFmtId. Probably related to its fonts:

<fonts count="3">
  <font>
    <sz val="11"/>
    <color rgb="FF000000"/>
    <name val="Calibri"/>
    <family val="2"/>
    <scheme val="minor"/>
  </font>
  <font/>
  <font>
    <b val="0"/>
    <i val="0"/>
    <strike val="0"/>
    <u val="none"/>
    <sz val="8"/>
    <color rgb="FF000000"/>
    <name val="Arial"/>
  </font>
</fonts>

This leads to @num_fmt_id being nil on line 36 in lib/saxlsx/style_collection_parser.rb. My patch simply calls to_i on @num_fmt_id which turns any nil into 0.

Missing <dimension> tag

I think using the <dimension> tag is a brilliant way to very quickly retrieve the number of rows, however some spreadsheets do not include this tag.

My patch adds a fallback, if the quick lookup failed it iterates through the rows.

I hope this PR meets your quality requirements and gets merged/released.

Thank you

[ebeigarts]

Hi, thanks, I have opened #11, that includes a much faster #count that looks for <dimension> or counts <row>. If <dimension> is missing, then it counts <row> without extra formatting/typecasting etc, this way it is much faster than each { @count += 1 }. Can you check #11?

[SGrondin]

I reviewed and approved #11