Fix null context GenBuffers

src/gpu/gl/GrGLCreateNullInterface.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "gl/GrGLInterface.h"
 #include "GrGLTestInterface.h"
@@ skipping 29 matching lines @@
 private:
     GrGLuint     fID;
     GrGLchar*    fDataPtr;
     GrGLsizeiptr fSize;         // size in bytes
     bool         fMapped;
 };
 
 // This class maintains a sparsely populated array of buffer pointers.
 class BufferManager {
 public:
-    BufferManager() : fFreeListHead(kFreeListEnd) {}
+    BufferManager() : fFreeListHead(kFreeListEnd) {
+        *fBuffers.append() = nullptr; // 0 is not a valid GL buffer id.
+    }
 
     ~BufferManager() {
         // nullptr out the entries that are really free list links rather than ptrs before deleting.
         intptr_t curr = fFreeListHead;
         while (kFreeListEnd != curr) {
             intptr_t next = reinterpret_cast<intptr_t>(fBuffers[SkToS32(curr)]);
             fBuffers[SkToS32(curr)] = nullptr;
             curr = next;
         }
 
@@ skipping 21 matching lines @@
             fFreeListHead = reinterpret_cast<intptr_t>(fBuffers[id]);
 
             buffer = new BufferObj(id);
             fBuffers[id] = buffer;
         }
 
         return buffer;
     }
 
     void free(BufferObj* buffer) {
+        SkASSERT(buffer);
         SkASSERT(fBuffers.count() > 0);
 
         GrGLuint id = buffer->id();
         delete buffer;
 
         fBuffers[id] = reinterpret_cast<BufferObj*>(fFreeListHead);
         fFreeListHead = id;
     }
 
 private:
@@ skipping 92 matching lines @@
             if (ids[i] == fCurrElementArrayBuffer) {
                 fCurrElementArrayBuffer = 0;
             }
             if (ids[i] == fCurrPixelPackBuffer) {
                 fCurrPixelPackBuffer = 0;
             }
             if (ids[i] == fCurrPixelUnpackBuffer) {
                 fCurrPixelUnpackBuffer = 0;
             }
 
-            BufferObj* buffer = fBufferManager.lookUp(ids[i]);
-            fBufferManager.free(buffer);
+            if (ids[i] > 0) {
+                BufferObj* buffer = fBufferManager.lookUp(ids[i]);
+                fBufferManager.free(buffer);
+            }
         }
     }
 
     GrGLvoid genFramebuffers(GrGLsizei n, GrGLuint *framebuffers) override {
         this->genGenericIds(n, framebuffers);
     }
 
     GrGLvoid genQueries(GrGLsizei n, GrGLuint *ids) override { this->genGenericIds(n, ids); }
 
     GrGLvoid genRenderbuffers(GrGLsizei n, GrGLuint *renderbuffers) override {
@@ skipping 385 matching lines @@
     "GL_ARB_timer_query",
     "GL_ARB_draw_buffers",
     "GL_ARB_occlusion_query",
     "GL_EXT_stencil_wrap",
     nullptr, // signifies the end of the array.
 };
 
 }  // anonymous namespace
 
 const GrGLInterface* GrGLCreateNullInterface() { return new NullInterface; }