LODSphereMesh: fix MSVC capture error in buildStitchTriangles

MSVC rejects using the constexpr locals N/stride inside the vid/snap lambdas
without an explicit capture (C3493), while capturing them trips Clang's
unused-capture warning. Reference the namespace-scope CHUNK_RES directly so no
capture is needed on either compiler.

Author: levinli303

src/celengine/lodspheremesh.cpp

@@ -239,15 +239,14 @@ static void
 buildStitchTriangles(int mask, std::vector<unsigned int>& out)
 {
     constexpr int N = CHUNK_RES;
-    constexpr auto stride = static_cast<unsigned int>(N + 1);
     auto vid = [](int a, int b) {
-        return static_cast<unsigned int>(a * static_cast<int>(stride) + b);
+        return static_cast<unsigned int>(a * (CHUNK_RES + 1) + b);
     };
     auto snap = [mask](int a, int b) {
         if (a == 0 && (mask & EDGE_LEFT)   != 0 && (b & 1) != 0) --b;
-        if (a == N && (mask & EDGE_RIGHT)  != 0 && (b & 1) != 0) --b;
+        if (a == CHUNK_RES && (mask & EDGE_RIGHT)  != 0 && (b & 1) != 0) --b;
         if (b == 0 && (mask & EDGE_BOTTOM) != 0 && (a & 1) != 0) --a;
-        if (b == N && (mask & EDGE_TOP)    != 0 && (a & 1) != 0) --a;
+        if (b == CHUNK_RES && (mask & EDGE_TOP)    != 0 && (a & 1) != 0) --a;
         return std::pair<int, int>(a, b);
     };