Calculator: Finish operation-in-progress only on new binary operations

[ronak69]

Calculator: Finish operation-in-progress only on new binary operations

Because of this the unary operations got applied to the result of the
operation-in-progress instead of the current argument as shown here:

    `16 + 9 <sqrt> =`
        Previous output: `sqrt(16 + 9)` = `5`
        Expected output: `16 + sqrt(9)` = `19`

this also fixes the following bug i found which i didn't mention in the commit message:

• do 5 * 5 = <MS>
• then 100 - <MR> = (output: -75 instead of 75)

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should i open issues for bugs even if i have a fix for it ready?