[hotfix] tonumber makes an empty string nil

frontend/version.lua

@@ -29,9 +29,9 @@ function Version:getNormalizedVersion(rev)
     if not rev then return end
     local year, month, revision = rev:match("v(%d%d%d%d)%.(%d%d)-?(%d*)")
 
-    if type(year) ~= "number" then revision = 0 end
-    if type(month) ~= "number" then revision = 0 end
-    if type(revision) ~= "number" then revision = 0 end
+    year = tonumber(year)
+    month = tonumber(month)
+    revision = tonumber(revision)
 
     local commit = rev:match("-%d*-g(%x*)[%d_%-]*")
     -- NOTE: * 10000 to handle at most 9999 commits since last tag ;).