Expose getFirstPatternCase, not getPatternCase/2

Author: smowton

java/ql/lib/semmle/code/java/ControlFlowGraph.qll

@@ -478,9 +478,9 @@ private module ControlFlowGraphImpl {
       or
       result instanceof NullDefaultCase
       or
-      not exists(getPatternCase(switch, _))
+      not exists(getFirstPatternCase(switch))
       or
-      result.getIndex() <= getPatternCase(switch, 0).getIndex()
+      result.getIndex() <= getFirstPatternCase(switch).getIndex()
     )
   }
 

java/ql/lib/semmle/code/java/controlflow/internal/SwitchCases.qll

@@ -5,11 +5,18 @@ import java
 /**
  * Gets the `i`th `PatternCase` defined on `switch`, if one exists.
  */
-PatternCase getPatternCase(StmtParent switch, int i) {
+private PatternCase getPatternCase(StmtParent switch, int i) {
   result =
     rank[i + 1](PatternCase pc, int caseIdx | pc.isNthCaseOf(switch, caseIdx) | pc order by caseIdx)
 }
 
+/**
+ * Gets the first `PatternCase` defined on `switch`, if one exists.
+ */
+PatternCase getFirstPatternCase(StmtParent switch) {
+  result = getPatternCase(switch, 0)
+}
+
 /**
  * Gets the PatternCase after pc, if one exists.
  */