Renderer: fix texture lookup paths + skip garbage Tile slots (r3)

[j92580498-max]

Fixes the two issues #2 reported running r2 on real Mavericks hardware.

1. All PNG textures rendered as flat coloured rectangles

loadTexture("gui/gui.png") was stripping both the directory and the extension before handing the result to [NSBundle pathForResource:ofType:]. Two problems with that:

• pathForResource:ofType: only looks in top-level Resources/ (and *.lproj children), but our bundle keeps the handheld/data/ layout, so the real files are at Resources/images/gui/gui.png, Resources/images/font/default8.png, Resources/images/terrain.png, etc.
• After stripping, two different files (gui/gui.png and gui/gui2.png) would also collide on the same lookup key.

Every texture call therefore fell to the LOGI("Couldn't find file:") branch and the renderer used its random-noise fallback — which is exactly the "buttons are coloured rectangles, no text" symptom the user reported.

Fix: keep the subdirectory and search a few likely Resources-relative directories with pathForResource:ofType:inDirectory:, falling back to the flat lookup for any iOS-style bundles, then to the dev-time data/images/ layout.

2. SIGSEGV in Chunk::rebuild() after loading any world

Crash log from #2 shows:

Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000001d10
Thread 0 Crashed:
0   com.mojang.minecraftpe.osx  Chunk::rebuild() + 640
1   com.mojang.minecraftpe.osx  LevelRenderer::updateDirtyChunks(...) + 414
2   com.mojang.minecraftpe.osx  GameRenderer::renderLevel(float) + 653

Disassembly of Chunk::rebuild + 640 lands on mov rax, qword ptr [rbx] where rbx is the value of Tile::tiles[tileId]. The slot isn't NULL — it's page-zero garbage (0x1d10). Boot diagnostics already warn that a few slots are inconsistent (Error: Missing category for tile 95/255), so the renderer now guards against both NULL and obviously-bogus sub-0x10000 pointers before dereferencing the vtable.

Test

• Cross-built via OSXCross + MacOSX10.9.sdk, -arch x86_64 -mmacosx-version-min=10.9 -stdlib=libstdc++.
• Output is Mach-O 64-bit x86_64 (NOUNDEFS | DYLDLINK | TWOLEVEL | WEAK_DEFINES | BINDS_TO_WEAK | PIE), 3.1 MB release.
• Bundle resources are confirmed nested correctly (Contents/Resources/images/gui/gui.png, etc.).
• Real-hardware verification has to be done by the issue reporter — I'll publish an r3 release tarball + checksums and ping Loading world crashes + not working textures i don't know why #2.