libstore/store-api: Do not query all substituters for substitutable path infos

This was broken in 11d7c80.

Author: xokdvium

src/libstore/store-api.cc

@@ -447,6 +447,8 @@ void Store::querySubstitutablePathInfos(const StorePathCAMap & paths, Substituta
                         .downloadSize = narInfo ? narInfo->fileSize : 0,
                         .narSize = info->narSize,
                     });
+
+                break; /* We are done. */
             } catch (InvalidPath &) {
             } catch (SubstituterDisabled &) {
             } catch (Error & e) {