handle conic underflow calc
handle conic underflow calc

w0 and w2 can both be non-zero, but w2*w0 can be zero -- unless we promote to doubles

Bug: oss-fuzz:6506
Change-Id: Id0716e22e1d989d2eb6d86417575cf917a31cb89
Reviewed-on: https://skia-review.googlesource.com/109480
Reviewed-by: Cary Clark <52792aa984ff6c4e9c802c7fa3093ed6a52a791f@google.com>
Commit-Queue: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>

Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,rubenvb/skia,google/skia,google/skia,google/skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,google/skia,rubenvb/skia,HalCanary/skia-hc,rubenvb/skia,aosp-mirror/platform_external_skia,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,rubenvb/skia,google/skia,HalCanary/skia-hc,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,rubenvb/skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,rubenvb/skia