Fixed decimal prompt weights without leading digit (#1182)

The regex was not accounting properly for prompt weights that didn't begin with a leading number such as .5 or .1 and was instead splitting those off into their own prompt which got everything all screwed up.

For example, the prompt string of "Fruit:1 grapes:-.5" should parse as
[('Fruit', 1.0), ('grapes', -.5)]
but was being incorrectly parsed as
[('Fruit', 1.0), ('grapes', 1.0), ('-.5', 1.0)]

This fixes that by making the regex properly catch decimals.

scripts/webui.py

@@ -1519,7 +1519,7 @@ prompt_parser = re.compile("""
     (?:             # non-capture group
     :+              # match one or more ':' characters
     (?P<weight>     # capture group for 'weight'
-    -?\d+(?:\.\d+)? # match positive or negative integer or decimal number
+    -?\d*\.{0,1}\d+ # match positive or negative integer or decimal number
     )?              # end weight capture group, make optional
     \s*             # strip spaces after weight
     |               # OR