docs/conf.py: Fix wrong assumption that missing prerelease.txt represents a release

Author: cameel

docs/conf.py

@@ -126,7 +126,7 @@ def get_github_username_repo(url):
 with open('../CMakeLists.txt', 'r', encoding='utf8') as f:
     version = re.search('PROJECT_VERSION "([^"]+)"', f.read()).group(1)
 # The full version, including alpha/beta/rc tags.
-if not os.path.isfile('../prerelease.txt') or os.path.getsize('../prerelease.txt') == 0:
+if os.path.isfile('../prerelease.txt') and os.path.getsize('../prerelease.txt') == 0:
     release = version
 else:
     # This is a prerelease version