Fix SpvExecutionModeOutputLinesEXT. (#5740)

Author: csyonghe

source/slang/slang-check-decl.cpp

@@ -8789,7 +8789,8 @@ void SemanticsDeclHeaderVisitor::checkMeshOutputDecl(VarDeclBase* varDecl)
         nullptr,
         ConstantFoldingKind::LinkTime,
         getSink());
-
+    if (!index)
+        return;
     Type* d = m_astBuilder->getMeshOutputTypeFromModifier(modifier, base, index);
     varDecl->type.type = d;
 }

source/slang/slang-emit-spirv.cpp

@@ -4467,7 +4467,7 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
                     if (t == "triangle")
                         m = SpvExecutionModeOutputTrianglesEXT;
                     else if (t == "line")
-                        m = SpvExecutionModeOutputTrianglesEXT;
+                        m = SpvExecutionModeOutputLinesEXT;
                     else if (t == "point")
                         m = SpvExecutionModeOutputPoints;
                 }