fix: if no previous prod release, return 1.0.0 if no prerelease

Here's an example of what this fixes: agrc/plpco-rdcc-notifications#147

src/utils.test.ts

@@ -38,6 +38,7 @@ describe('getNewVersion', () => {
     ['0.1.0-0', 'minor', true, null, '0.1.0-1'],
     ['2.0.0-5', 'minor', false, '1.3.4', '1.4.0'],
     [null, 'patch', false, null, '1.0.0'],
+    ['1.0.0-3', 'patch', false, null, '1.0.0'],
   ];
 
   test.each(cases)('%s, %s, %j, %s => %s', (lastTag, bumpType, prerelease, lastProdTag, expectation) => {

src/utils.ts

@@ -18,6 +18,10 @@ export function getNewVersion(
     return prerelease ? '1.0.0-0' : '1.0.0';
   }
 
+  if (!prerelease && !lastProdTag) {
+    return '1.0.0';
+  }
+
   /* If the last tag was a major prerelease, we shouldn't
   bump anything but the prerelease number. For example, if the
   last tag was 2.0.0-0 and this is a minor bump, we should
@@ -29,7 +33,7 @@ export function getNewVersion(
 
   const releaseType = getReleaseType(lastTag, conventionalReleaseType, prerelease, lastProdTag);
 
-  return semver.inc(prerelease ? lastTag : lastProdTag ?? '0.0.0', releaseType, prerelease);
+  return semver.inc(prerelease ? lastTag : lastProdTag ?? '1.0.0', releaseType, prerelease);
 }
 
 function getReleaseType(