mmaprototype: use >= 0 for emptyVoterConstraintIndex

This commit fixes >= 0 when checking for whether there were
valid emptyVoterConstraintIndex and emptyConstraintIndex
since 0 is a valid index.

Author: wenyihu6

pkg/kv/kvserver/allocator/mmaprototype/constraint.go

@@ -605,7 +605,7 @@ func doStructuralNormalization(conf *normalizedSpanConfig) error {
 	// has some remainingReplicas, we take them here to satisfy the empty voter
 	// constraint as much as possible. Only what is remaining in the empty voter
 	// constraint will then be available for subsequent narrowing.
-	if emptyVoterConstraintIndex > 0 && emptyConstraintIndex > 0 {
+	if emptyVoterConstraintIndex >= 0 && emptyConstraintIndex >= 0 {
 		neededReplicas := conf.voterConstraints[emptyVoterConstraintIndex].numReplicas
 		if voterConstraints[emptyVoterConstraintIndex].numReplicas != 0 {
 			panic("programming error")

pkg/kv/kvserver/allocator/mmaprototype/testdata/normalize_config

@@ -609,8 +609,6 @@ output:
 
 # Replicas are not constrained. The voter constraints are promoted to replica
 # constraints.
-#
-# TODO(sumeer): investigate why the normalization also threw an error.
 normalize num-replicas=5 num-voters=3
 constraint num-replicas=5
 voter-constraint num-replicas=1 +region=a +zone=a1
@@ -623,7 +621,6 @@ input:
  voter-constraints:
    +region=a,+zone=a1:1
    +region=a,+zone=a2:1
-err=could not satisfy all voter constraints due to non-intersecting conjunctions in voter and all replica constraints
 output:
  num-replicas=5 num-voters=3
  constraints: