Flash Attention Enabled Incorrectly Due to Fallback in Head Count Metadata

### What is the issue? When loading a model that lacks metadata for `attention.key_length` and `attention.value_length`, the fallback mechanism in the `kv.Uint` function returns the embedding head count for both fields. This causes the check in `SupportsFlashAttention()`, which compares the key and value head counts, to show success incorrectly (since both values are identical), even if the model does not truly support Flash Attention. As a result, Flash Attention is enabled, leading to issues such as segmentation faults (e.g., SIGSEGV in `llama/ggml-cuda/fattn.cu:67`). **Steps to Reproduce:** 1. Load a model that does not include `attention.key_length` and `attention.value_length` in its metadata. 2. Observe that the functions `EmbeddingHeadCountK()` and `EmbeddingHeadCountV()` fallback to the embedding head count. 3. The `SupportsFlashAttention()` method then compares these equal values and incorrectly concludes that the model supports Flash Attention. 4. Enabling Flash Attention under these conditions leads to crashes (segmentation faults). **Expected Behavior:** If the model metadata is missing `attention.key_length` and `attention.value_length`, the server should disable Flash Attention by default. ### Relevant log output ```shell ``` ### OS _No response_ ### GPU _No response_ ### CPU _No response_ ### Ollama version _No response_