Fail if cannot construct a valid schema

Summary:
We would get an infinite loop under certain circumstances because we store an error value in one of the fields of the `DbSchema` type. See D56519258 for full diagnosis.

This diff makes sure to just fail early if we cannot load an `all` schema.

Reviewed By: bochko

Differential Revision: D56531547

fbshipit-source-id: 2e51946224a4fd2c05369c910988b18080472a84

glean/db/Glean/Database/Schema.hs

@@ -474,11 +474,12 @@ mkDbSchema toList cacheVar knownPids dbContent
         legacyAllVersions =
           hashedSchemaAllVersions $ procSchemaHashed latestSchema
 
-        latestSchemaId =
-          case IntMap.lookupMax legacyAllVersions of
-            Nothing -> error "no \"all\" schema"
-            Just (_, id) -> id
+    latestSchemaId <-
+        case IntMap.lookupMax legacyAllVersions of
+            Nothing -> throwIO $ ErrorCall "no \"all\" schema"
+            Just (_, id) -> return id
 
+    let
         dbSchemaId =
           case IntMap.lookupMax (hashedSchemaAllVersions stored) of
             Nothing -> error "no \"all\" schema in DB"