Clamp out of range values in K quantizer

This assertion fails when quantizing Mixtral 8x7b as Q5_K_M, because I
used `convert.py --outtype f32` and the Mixtral weights use bf16 which
has a much larger exponent range than the K quantizer is expecting. If
--outtype f16 is used then the assert doesn't fail.

See ggerganov/llama.cpp#2982

ggml-quants.c

@@ -1023,7 +1023,7 @@ void dequantize_row_q8_0(const block_q8_0 * restrict x, float * restrict y, int6
 // ===================== Helper functions
 //
 static inline int nearest_int(float fval) {
-    assert(fval <= 4194303.f);
+    fval = fminf(fval, 4194303.f);
     float val = fval + 12582912.f;
     int i; memcpy(&i, &val, sizeof(int));
     return (i & 0x007fffff) - 0x00400000;