Flood Filling Crashes

Attempting to build sample art for IF Engine, I pretty handily crashed the flood fill algorithm:

# Reset Palette, Clear Screen to White, Draw in Black
# Hacky Border because we can't hit 319 yet.
R
C 0
E
C 15
S 0 0 255 199
C 0

# Horizon
L 0 87 255 87

# Sun
L 255 64 248 61 240 61 233 62 228 66 223 72 220 78 220 87

# Beach
L 0 101 87 124 126 128 148 133 160 136 168 141 172 146 171 149 169 153 169 158 176 164 188 168 205 171 227 174 255 174

# Fill Sun
C 12
F 242 74

# Fill Beach
C 14
F 105 161

# Fill Ocean
C 1
F 194 106