Check for an invalid emscripten-sbrk-ptr. Would have helped detect the SAFE_HEAP/SIDE_MODULE bug

src/passes/PostEmscripten.cpp

diff --git a/src/passes/PostEmscripten.cpp b/src/passes/PostEmscripten.cpp
index 8efaae8..65404ba 100644
--- a/src/passes/PostEmscripten.cpp
+++ b/src/passes/PostEmscripten.cpp
@@ -80,6 +80,9 @@
       runner->options.getArgumentOrDefault("emscripten-sbrk-ptr", "");
     if (sbrkPtrStr != "") {
       auto sbrkPtr = std::stoi(sbrkPtrStr);
+      if (sbrkPtr == 0 || sbrkPtr == -1) {
+        Fatal() << "Invalid value for emscripten-sbrk-ptr";
+      }
       ImportInfo imports(*module);
       auto* func = imports.getImportedFunction(ENV, "emscripten_get_sbrk_ptr");
       if (func) {