Merge #153: Define MAX_DIGITS_BTC for magic number in BitcoinUnits::f…

…ormat

198fff8 GUI: Define MAX_DIGITS_BTC for magic number in BitcoinUnits::format (Luke Dashjr)

Pull request description:

  A magic number snuck in with bitcoin/bitcoin#16432

ACKs for top commit:
  hebasto:
    ACK 198fff8, I have reviewed the code and it looks OK, I agree it can be merged.
  kristapsk:
    utACK 198fff8

Tree-SHA512: 78dc23c2ae61bac41e5e34eebf57274599cb2ebb0b18d46e8a3228d42b256a1bc9bb17091c748f0f692ef1c4c241cfbd3e30a12bcd12222a234c1a9547ebe786

src/qt/bitcoinunits.cpp

@@ -8,6 +8,8 @@
 
 #include <cassert>
 
+static constexpr auto MAX_DIGITS_BTC = 16;
+
 BitcoinUnits::BitcoinUnits(QObject *parent):
         QAbstractListModel(parent),
         unitlist(availableUnits())
@@ -108,7 +110,9 @@ QString BitcoinUnits::format(int unit, const CAmount& nIn, bool fPlus, Separator
     qint64 n_abs = (n > 0 ? n : -n);
     qint64 quotient = n_abs / coin;
     QString quotient_str = QString::number(quotient);
-    if (justify) quotient_str = quotient_str.rightJustified(16 - num_decimals, ' ');
+    if (justify) {
+        quotient_str = quotient_str.rightJustified(MAX_DIGITS_BTC - num_decimals, ' ');
+    }
 
     // Use SI-style thin space separators as these are locale independent and can't be
     // confused with the decimal marker.