Fix ValueError while accessing cell._tc.bottom#1526

Witiko wants to merge 2 commits intopython-openxml:masterpython-openxml/python-docx:masterfrom

Witiko:fix/value-error-no-tc-element-at-grid-offsetWitiko/python-docx:fix/value-error-no-tc-element-at-grid-offsetCopy head branch name to clipboard