The ornamental design for a golfballretriever, as shown and described.
1. Golf ball retriever
1.1: Front
1.2: Back
1.3: Top
1.4: Bottom
1.5: Right
1.6: Left
1.7: Perspective
1.1: front view of the golf ball retriever; 1.2: back view of the golf ball retriever; 1.3: top plan view of the golf ball retriever; 1.4: bottom plan view of the golf ball retriever; 1.5: right side view of the golf ball retriever; 1.6: left side view of the golf ball retriever; 1.7: front perspective view of the golf ball retriever.