added exception for incorrect board name string

Author: CatherineH

src/arduino.cc/builder/constants/constants.go

@@ -211,6 +211,7 @@ const MSG_BOARD_UNKNOWN = "Board {0} (platform {1}, package {2}) is unknown"
 const MSG_BOOTLOADER_FILE_MISSING = "Bootloader file specified but missing: {0}"
 const MSG_BUILD_OPTIONS_CHANGED = "Build options changed, rebuilding all"
 const MSG_CANT_FIND_SKETCH_IN_PATH = "Unable to find {0} in {1}"
+const MSG_FQBN_INVALID = "{0} is not a valid fully qualified board name. Required format is targetPackageName:targetPlatformName:targetBoardName."
 const MSG_INVALID_QUOTING = "Invalid quoting: no closing [{0}] char found."
 const MSG_LIB_LEGACY = "(legacy)"
 const MSG_LIBRARIES_MULTIPLE_LIBS_FOUND_FOR = "Multiple libraries were found for \"{0}\""

src/arduino.cc/builder/target_board_resolver.go

@@ -42,6 +42,9 @@ func (s *TargetBoardResolver) Run(context map[string]interface{}) error {
 	fqbn := context[constants.CTX_FQBN].(string)
 
 	fqbnParts := strings.Split(fqbn, ":")
+	if len(fqbnParts) < 3 {
+		return utils.Errorf(context, constants.MSG_FQBN_INVALID, fqbn)
+	}
 	targetPackageName := fqbnParts[0]
 	targetPlatformName := fqbnParts[1]
 	targetBoardName := fqbnParts[2]