Nikkei edges up as weak yen helps mood; China PMI, Japan earnings in focus

* Volume may be low as market focused on China survey, Japanese earnings * Canon Marketing tumbles to 2-month low on possible erroneous order - traders By Ayai Tomisawa TOKYO, July 24 (Reuters) - Japan's Nikkei share average edged up on Thursday morning as the slightly weakening yen supported sentiment, but geopolitical worries over Ukraine and Gaza kept activity in check. Investors stayed on the sidelines as they were also focused on a manufacturing survey from China later in t