plumbing: object, rename calculation uses too much memory

The size of the similarity matrix is not limited and can be quite big
when lots of files are deleted and added in a commit.

Signed-off-by: Javi Fontan <jfontan@gmail.com>
(cherry picked from commit 1115cb6)

plumbing/object/rename.go

@@ -403,10 +403,16 @@ func min(a, b int) int {
 	return b
 }
 
+const maxMatrixSize = 10000
+
 func buildSimilarityMatrix(srcs, dsts []*Change, renameScore int) (similarityMatrix, error) {
 	// Allocate for the worst-case scenario where every pair has a score
 	// that we need to consider. We might not need that many.
-	matrix := make(similarityMatrix, 0, len(srcs)*len(dsts))
+	matrixSize := len(srcs) * len(dsts)
+	if matrixSize > maxMatrixSize {
+		matrixSize = maxMatrixSize
+	}
+	matrix := make(similarityMatrix, 0, matrixSize)
 	srcSizes := make([]int64, len(srcs))
 	dstSizes := make([]int64, len(dsts))
 	dstTooLarge := make(map[int]bool)