Continue mirror extension versions even if one fails

Currently, the OpenVSX server stops mirroring extension version if one of the
versions failed to be mirrored. This commit logs the mirror failure instead of
throwing an error.

Fixes eclipse#923.

server/src/main/java/org/eclipse/openvsx/mirror/MirrorExtensionService.java

@@ -142,8 +142,8 @@ private void mirrorExtensionVersions(String namespaceName, String extensionName,
                 mirrorExtensionVersion(json);
                 data.getMirroredVersions().increment();
             } catch (Throwable t) {
+                jobContext.logger().info("failure to mirror " + NamingUtil.toLogFormat(json) + " (" + (i+1) + "/" +  toAdd.size() + ")");
                 data.getFailedVersions().increment();
-                throw t;
             }
         }
     }