preprocessor: guard against OOB read in handlePragma for #pragma STDGL

When a shader contains '#pragma STDGL' with fewer than 4 tokens, the
condition at ParseHelper.cpp:422 accessed tokens[1] and tokens[3]
without first checking tokens.size(), causing an out-of-bounds read
and a SEGV under AddressSanitizer.

Every other tokens[N] access in handlePragma() already has an explicit
size check (see lines 340, 366). Apply the same guard here:

  } else if (spvVersion.spv > 0 && tokens[0].compare("STDGL") == 0 &&
             tokens.size() >= 4 &&
             tokens[1].compare("invariant") == 0 &&
             tokens[3].compare("all") == 0) {

Minimal reproducer (15 bytes, requires Vulkan/SPIR-V target):
  #pragma STDGL

Found by libFuzzer + ASan on fuzz_glslang_direct harness.

Fixes: SEGV in glslang::TParseContext::handlePragma() (ParseHelper.cpp:422)

Author: ashketchumwashere

Test/baseResults/spv.pragma.stdgl.oob.vert.out

@@ -0,0 +1,17 @@
+spv.pragma.stdgl.oob.vert
+// Module Version 10000
+// Generated by (magic number): 8000b
+// Id's are bound by 6
+
+                              Capability Shader
+               1:             ExtInstImport  "GLSL.std.450"
+                              MemoryModel Logical GLSL450
+                              EntryPoint Vertex 4  "main"
+                              Source GLSL 450
+                              Name 4  "main"
+               2:             TypeVoid
+               3:             TypeFunction 2
+         4(main):           2 Function None 3
+               5:             Label
+                              Return
+                              FunctionEnd

Test/spv.pragma.stdgl.oob.vert

@@ -0,0 +1,8 @@
+#version 450
+// Regression test: #pragma STDGL with fewer than 4 tokens must not OOB-read
+// tokens[1]/tokens[3] in handlePragma() — fixed by checking tokens.size() >= 4
+// before accessing them (ParseHelper.cpp).
+#pragma STDGL
+#pragma STDGL invariant
+#pragma STDGL invariant(
+void main() {}

glslang/MachineIndependent/ParseHelper.cpp

@@ -419,6 +419,7 @@ void TParseContext::handlePragma(const TSourceLoc& loc, const TVector<TString>&
     } else if (tokens[0].compare("glslang_binary_double_output") == 0) {
         intermediate.setBinaryDoubleOutput();
     } else if (spvVersion.spv > 0 && tokens[0].compare("STDGL") == 0 &&
+               tokens.size() >= 4 &&
                tokens[1].compare("invariant") == 0 && tokens[3].compare("all") == 0) {
         intermediate.setInvariantAll();
         // Set all builtin out variables invariant if declared

gtests/Spv.FromFile.cpp

@@ -315,6 +315,7 @@ INSTANTIATE_TEST_SUITE_P(
         "spv.for-nobody.vert",
         "spv.while-continue-break.vert",
         "spv.while-simple.vert",
+        "spv.pragma.stdgl.oob.vert",
         // vulkan-specific tests
         "rayQuery.rgen",
         "rayQuery-no-cse.rgen",