Fix indents containing a half-tab

Now also lines that are indented with a few spaces + a half-tab (tab equal to 2 spaces) are fixed correctly. This weird indentation is present for example in a lot of files of the Opencart project (github.com/opencart/opencart).

For example: (space)(space)(tab) becomes 6 spaces in the old version, but it should be converted to 4 spaces since indents can only be multiples of 4 spaces. This problem can occur when a texteditor's tabsize is set to 2 and the writer uses tabs while the existing indents are spaces.