Changed to call EnsureStorage() unconditionally.

If EnsureStorage() is called unconditionally, the array will be expanded, so the position will never become negative. When the conditions inside EnsureStorage() are true, it might be necessary to expand the array, regardless of the comparison between newpos and codepos.

https://github.com/dotnet/runtime/blob/6ebc8bd86dbc780b2a2a7daf3ab6020f9104f09e/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.MultipleMatches.Tests.cs#L461-L469

Before the change, in this test case, EnsureStorage() is not called because newpos == codepos == 6 from the first time until an exception occurs.

Fix dotnet#62049

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexInterpreter.cs

@@ -53,10 +53,7 @@ private void Advance(int i)
         private void Goto(int newpos)
         {
             // When branching backward, ensure storage.
-            if (newpos < _codepos)
-            {
-                EnsureStorage();
-            }
+            EnsureStorage();
 
             _codepos = newpos;
             SetOperator((RegexOpcode)_code.Codes[newpos]);
@@ -74,15 +71,8 @@ private void TrackPush(int i1)
             int[] localruntrack = runtrack!;
             int localruntrackpos = runtrackpos;
 
-            if (localruntrackpos > 1)
-            {
-                localruntrack[--localruntrackpos] = i1;
-                localruntrack[--localruntrackpos] = _codepos;
-            }
-            else
-            {
-                localruntrackpos = 0;
-            }
+            localruntrack[--localruntrackpos] = i1;
+            localruntrack[--localruntrackpos] = _codepos;
 
             runtrackpos = localruntrackpos;
         }
@@ -128,16 +118,9 @@ private void TrackPush2(int i1, int i2)
             int[] localruntrack = runtrack!;
             int localruntrackpos = runtrackpos;
 
-            if (localruntrackpos > 2)
-            {
-                localruntrack[--localruntrackpos] = i1;
-                localruntrack[--localruntrackpos] = i2;
-                localruntrack[--localruntrackpos] = -_codepos;
-            }
-            else
-            {
-                localruntrackpos = 0;
-            }
+            localruntrack[--localruntrackpos] = i1;
+            localruntrack[--localruntrackpos] = i2;
+            localruntrack[--localruntrackpos] = -_codepos;
 
             runtrackpos = localruntrackpos;
         }
@@ -158,10 +141,7 @@ private void Backtrack()
             SetOperator((RegexOpcode)(_code.Codes[newpos] | back));
 
             // When branching backward, ensure storage.
-            if (newpos < _codepos)
-            {
-                EnsureStorage();
-            }
+            EnsureStorage();
 
             _codepos = newpos;
         }