title: Openpyxl finds merged cells even though there are none
body: <p>I'm handling excels in my python script and get the following error:</p>
  
  <pre><code>    Traceback (most recent call last):
    File "script_consolidateExcels_v3.py", line 134, in &lt;module&gt;
      colNum = findColOfCell(ws, "xxx", 1)
    File "script_consolidateExcels_v3.py", line 28, in findColOfCell
      if worksheet.cell(row=inRow, column=k).value == val:
  AttributeError: 'MergedCell' object has no attribute 'value'
  </code></pre>
  
  <p>The excel file initially had merged cells, but I unmerged everything using Microsoft Excel, yet this error still pops up. I even tried ws.unmerge_cells(), but with no help. (Weirdly enough, at first I wrote and run the script on a windows laptop and this error did not pop up... I sent the script to my mac, and now I get this error... (I can't access the windows laptop currently))</p>
  
  <p>Here is the problematic part:</p>
  
  <pre><code>def findColOfCell(worksheet, val, inRow, startCol=1):
      i = 0
      k = startCol
      while i == 0:
          if worksheet.cell(row=inRow, column=k).value == val:
              i = 1
              # here = ord(worksheet.cell(row=inRow, column=k).column)-64 # convert column letter to number
              here = worksheet.cell(row=inRow, column=k).column
          else: k += 1
      return here
  </code></pre>