Fix compilation error when Esp.h is included first in sketch (#590)
Fix compilation error when Esp.h is included first in sketch (#590)

CanTireInnovations/Arduino,wemos/Arduino,wemos/Arduino,CanTireInnovations/Arduino,Cloudino/Cloudino-Arduino-IDE,Adam5Wu/Arduino,lrmoreno007/Arduino,Lan-Hekary/Arduino,Cloudino/Arduino,KaloNK/Arduino,CanTireInnovations/Arduino,hallard/Arduino,KaloNK/Arduino,wemos/Arduino,toastedcode/esp8266-Arduino,esp8266/Arduino,Links2004/Arduino,lrmoreno007/Arduino,gguuss/Arduino,chrisfraser/Arduino,Cloudino/Arduino,CanTireInnovations/Arduino,esp8266/Arduino,NullMedia/Arduino,me-no-dev/Arduino,chrisfraser/Arduino,lrmoreno007/Arduino,Cloudino/Cloudino-Arduino-IDE,NextDevBoard/Arduino,Links2004/Arduino,Cloudino/Arduino,NextDevBoard/Arduino,gguuss/Arduino,Cloudino/Arduino,gguuss/Arduino,Adam5Wu/Arduino,Links2004/Arduino,lrmoreno007/Arduino,Cloudino/Cloudino-Arduino-IDE,Cloudino/Cloudino-Arduino-IDE,toastedcode/esp8266-Arduino,jes/Arduino,jes/Arduino,quertenmont/Arduino,Cloudino/Cloudino-Arduino-IDE,edog1973/Arduino,Juppit/Arduino,hallard/Arduino,NullMedia/Arduino,hallard/Arduino,me-no-dev/Arduino,jes/Arduino,martinayotte/ESP8266-Arduino,esp8266/Arduino,toastedcode/esp8266-Arduino,me-no-dev/Arduino,edog1973/Arduino,quertenmont/Arduino,wemos/Arduino,Lan-Hekary/Arduino,edog1973/Arduino,jes/Arduino,KaloNK/Arduino,edog1973/Arduino,me-no-dev/Arduino,Adam5Wu/Arduino,NullMedia/Arduino,chrisfraser/Arduino,Lan-Hekary/Arduino,martinayotte/ESP8266-Arduino,KaloNK/Arduino,martinayotte/ESP8266-Arduino,lrmoreno007/Arduino,Cloudino/Cloudino-Arduino-IDE,Cloudino/Arduino,gguuss/Arduino,esp8266/Arduino,Juppit/Arduino,Cloudino/Arduino,sticilface/Arduino,Lan-Hekary/Arduino,NullMedia/Arduino,edog1973/Arduino,gguuss/Arduino,wemos/Arduino,Cloudino/Arduino,quertenmont/Arduino,me-no-dev/Arduino,Adam5Wu/Arduino,NextDevBoard/Arduino,chrisfraser/Arduino,esp8266/Arduino,Links2004/Arduino,quertenmont/Arduino,hallard/Arduino,Adam5Wu/Arduino,Juppit/Arduino,sticilface/Arduino,jes/Arduino,NextDevBoard/Arduino,CanTireInnovations/Arduino,NextDevBoard/Arduino,Cloudino/Cloudino-Arduino-IDE,CanTireInnovations/Arduino,sticilface/Arduino,NullMedia/Arduino,hallard/Arduino,Juppit/Arduino,martinayotte/ESP8266-Arduino,Links2004/Arduino,quertenmont/Arduino,toastedcode/esp8266-Arduino,chrisfraser/Arduino,Juppit/Arduino,toastedcode/esp8266-Arduino,KaloNK/Arduino,sticilface/Arduino,sticilface/Arduino,Lan-Hekary/Arduino,martinayotte/ESP8266-Arduino,CanTireInnovations/Arduino