Explicitly shown carbons disappearing on molecule saving

**Steps to Reproduce**
1. Draw molecule with implicit carbons
2. Go to Settings > Atoms and enable the "Display carbon explicitly" option.
3. Note carbons become displayed
4. Try to export image data using some javascript (Note there is no way to set explicit Carbons via API)

**Actual behavior**
carbons not included

**Expected behavior**
exported exact same image as displayed

**Ketcher version**
3.7.0

**Test case**

//producing SVG output

ketcher.getMolfile('v3000').then(molfile => {
return ketcher.setMolecule(molfile)
.then(() => ketcher.layout());

}).then(() => {
// Once the molecule is laid out with explicit hydrogens, get the updated molecule file.
return ketcher.getMolfile('v3000');

}).then(updatedMolfile => {
// Generate the SVG image from the *updated* molecule data
return ketcher.generateImage(updatedMolfile, {
outputFormat: 'svg'
});

}).then(svgBlob => {
const reader = new FileReader();
reader.onload = function() {

let svgString = reader.result;

console.log("SVG = " + svgString);

};
reader.readAsText(svgBlob);
}).catch(error => {
console.error('Error retrieving SVG from Ketcher:', error);
});