vm: initialize unused native call arguments - #436

VM_Call's native path initializes only nargs elements of args[3] but always reads all three when calling entryPoint. Zero-, one- and two-argument calls therefore read uninitialized integers. Clang 21's optimized zero-count call enters an unbounded argument-copy loop and crashes before bot startup.

Initialize the array so unused slots are zero. The included production-body C regression calls a native entry stub with counts 3, 0, 1 and 2 and checks every slot, return value and call depth. It segfaults before and passes after with Clang; its header contains the build/run command. The C++ fork's GCC and Clang tests also pass, and native bot smoke now matches QVM output on both Quake 3 maps. No floating-point expression or golden changes.